Support sign in tagfocus (#438)

Support sign in tagfocus

internal/driver/driver_focus.go

 	"github.com/google/pprof/profile"
 )
 
-var tagFilterRangeRx = regexp.MustCompile("([[:digit:]]+)([[:alpha:]]+)")
+var tagFilterRangeRx = regexp.MustCompile("([+-]?[[:digit:]]+)([[:alpha:]]+)")
 
 // applyFocus filters samples based on the focus/ignore options
 func applyFocus(prof *profile.Profile, numLabelUnits map[string]string, v variables, ui plugin.UI) error {

internal/driver/driver_test.go

 		{"peek=line.*01", "cpu"},
 		{"weblist=line[13],addresses,flat", "cpu"},
 		{"tags,tagfocus=400kb:", "heap_request"},
+		{"tags,tagfocus=+400kb:", "heap_request"},
 		{"dot", "longNameFuncs"},
 		{"text", "longNameFuncs"},
 	}
 			map[string]string{"key1": "bytes"},
 			false,
 		},
+		{
+			"Match negative key and range of values, value matches",
+			"bytes=-512b:-128b",
+			map[string][]int64{"bytes": {-256}},
+			map[string]string{"bytes": "bytes"},
+			true,
+		},
+		{
+			"Match negative key and range of values, value outside range",
+			"bytes=-512b:-128b",
+			map[string][]int64{"bytes": {-2048}},
+			map[string]string{"bytes": "bytes"},
+			false,
+		},
 	}
 	for _, test := range tagFilterTests {
 		t.Run(test.desc, func(*testing.T) {