Add command-line editing support for interactive pprof

This implements basic command-line editing, using
github.com/chzyer/readline. This will not affect the golang
distribution as it uses its own pprof driver, with its own
driver.

Only tested on Linux.
TODO: Implement auto-completion and persistent history.

The code was updated in #335 but the doc wasn't updated. Also the doc
didn't include $path which is searched as well, see locateBinaries in
internal/driver/fetch.go.

Fixes #342.

Trying to test against /debug/pprof/profile has been giving some flakes
and trouble so far (#146, #253, #328, golang/go#24611, golang/go#22594). While
some of the discussions the failures triggered appear to be useful (such
as whether CPU profiles are expected to be working on Windows XP or
not), that kind of testing is not really in the scope for this
particular test. This change switches the test to use goroutine profile
instead which is hopefully much less dependent on the environment. The
change also makes the test much faster to run.

Previously, the web UI was hard-coded to be served at `/` but
applications which are *embedding* the ui are unlikely to host it there.

This change makes the links between the various ui pages relative,
addressing this problem.

To make sure this doesn't rot, the internal http server now serves the
ui at /ui/ (redirecting there from the root).

I think we can all agree that the ui code and JavaScript is kind of a
haphazard affair. I performed a great deal of clicking around to make
sure the semantics didn't change and interestingly spent some time
trying to fix semantics I later realized weren't actually there: I
thought that when navigating to another page from a focused search (say
`flamegraph?f=x`) the focus would be carried over. This doesn't seem to
be the case, however.

The point being, there's no test coverage and setting it up is way
beyond what I can do here. I'm happy to manually verify whatever
sequence of clicks is suggested, though.

Touches https://github.com/cockroachdb/cockroach/pull/24145.

This fixes a bug introduced in #341 which caused the browser
opening code to be disabled for the standard `pprof -http`
invocation.

Introduce a proper getter on the UI which determines whether
the browser ought to be opened.

* Avoid opening browser when not in terminal

This also reverts e82ee9a, though only in spirit since the revert
did not apply cleanly.

This change may look cosmetic, but note that `plugin.UI` can be
passed in from the outside. This is important for embedding pprof
into an application for easy access to the web ui: with this change,
such an application can pass a non-Terminal `profile.UI` and avoids
the browser code.

* Allow passing in a custom HTTPServer

This allows embedding the pprof ui into an existing application.
See https://github.com/cockroachdb/cockroach/pull/24145 for an example.

* Add tests for source file searching.

* Fix slash handling in tests on Windows.

* Fix test cleanup, it was leaving stale files.

* Fix number of args in Fatalf call

In the interactive mode, inform users of different sample types
if the profile includes zero samples for selected sample type
by default (or through user-provided sample_index flag value).

The example output may look like

$ pprof mem.prof
Type: inuse_space
Time: Mar 20, 2018 at 11:36am (EDT)

No samples were found with the default sample value type.
Try "sample_index" command to analyze different sample values.

Entering interactive mode (type "help" for commands, "o" for options)
(pprof)

Update golang/go#24443

Update perf_to_profile cli arguments to use flags. (#277)

Fixes #277

As perf_to_profile uses flags to parse its arguments, modify the call to perf_to_profile to use flags. Also pass the '-f' flag to overwrite the existing output profile file.
Redirect perf_to_profile's stdout/stderr to pprof's stdout/stderr.

Use o.Writer if not nil to write output

Remove duplicate word "the"

Install graphviz on xcode7.3 and xcode8.3 travis builds

Set base address on OSX.

This fixes issue #311. The mapped address of libraries was never considered, nor was the load address of the segments. It also fixes a couple of issues in binutils.go, such as when the tail of the data wasn't handled right when grouping symbols at the same address.

* fix TestWebInterface

* check errors in modified portion of TestWebInterface

* use defer wg.Done()

* use random port when no port specified

* remove debugging print statement

The test overrides $HOME now so the checks are not needed now.

This change detects concatenated profiles by checking if time_nanos appears more than once in the profile being parsed.

Fixes #273

Debian builds packages with HOME set to a bogus value and this causes tests to
fail when packaging Go 1.10...

When pprof symbolizes kernel addresses in vmlinux binary for a profile
converted using https://github.com/google/perf_data_converter, the
addresses need to be adjusted if kernel ASLR is in effect. So far the
call to GetBase did not pass text segment info to GetBase which
shortcircuited the code to merely return zero adjustment. This change
fixes the call to GetBase to address that.

The added test case is a simulation of what happens with vmlinux, but it
should be pretty close. Including a vmlinux file into the test data does
not appear practical due to the binary size. I verified that the test
failed before the fix and passes after.

Note that the fixed issue is specific to the kernel ASLR as user-mode
ASRL-enabled binaries (i.e. built with -pie / -fpie) have ET_DYN type
which takes a different code path in GetBase which did not have issues
before this fix in practice.

The current version of go vet does not flag these as noted in
golang/go#23539. A fix is in the works, and will likely be included in
Go 1.11. Make the updated vet tool happy, so that the vendored copy of
pprof in the Go tree can be updated and make the vet trybot happy.

Fixes #297.

* Support parsing of is_folded bit

* Include folded bit lin (*Location).string() and in profile mergining

* address comments

* Set IsFolded to false during symbolization when Line is reset

* simplify tests

On an instance of the Android emulator running x86_64, $HOME points
to / which is not writable. Add Android to the list of GOOS where
the temp dir error is skipped.

Fixes the android/amd64 and android/386 builders on build.golang.org.

* Fix panic on merge when one profile missing mappings

* Simplify fix for merge panics

Pull request #263 disabled the refine menu for any views other than
Graph, but that's not expected - it's perfectly fine to use it for Flame
and Top, so just keep it enabled.

Fixes #285.

The third_party svg directory has been a mix of pprof-specific code and
svgpan itself. This change moves the pprof-specific code out and adds a
license file. It also updates svgpan to 1.2.2 from
https://github.com/aleofreddi/svgpan while we are here. It also renames
the directory to svgpan to have all directories under third_party be
named precisely over the third party package they hold.

Change URL matching code to restore compatibility with old pprof (#276)

* Add documentation on getting the source.

* Update the doc more.