cmd/trace/v2: handle the -pprof flag

Turns out we ported all the profile generation, but forgot to actually
support the command line flags for them! This change fixes the issue by
handling the different kinds of profiles and writing them out to stdout.

Fixes #66782.

Change-Id: I7756fb4636ce8daaf11ed471be79c86ce3d463cc
Reviewed-on: https://go-review.googlesource.com/c/go/+/578318
Reviewed-by: Carlos Amedee <carlos@golang.org>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/cmd/trace/v2/main.go

@@ -28,6 +28,35 @@ func Main(traceFile, httpAddr, pprof string, debug int) error {
 	}
 	defer tracef.Close()
 
+	// Handle requests for profiles.
+	if pprof != "" {
+		parsed, err := parseTrace(tracef)
+		if err != nil {
+			return err
+		}
+		var f traceviewer.ProfileFunc
+		switch pprof {
+		case "net":
+			f = pprofByGoroutine(computePprofIO(), parsed)
+		case "sync":
+			f = pprofByGoroutine(computePprofBlock(), parsed)
+		case "syscall":
+			f = pprofByGoroutine(computePprofSyscall(), parsed)
+		case "sched":
+			f = pprofByGoroutine(computePprofSched(), parsed)
+		default:
+			return fmt.Errorf("unknown pprof type %s\n", pprof)
+		}
+		records, err := f(&http.Request{})
+		if err != nil {
+			return fmt.Errorf("failed to generate pprof: %v\n", err)
+		}
+		if err := traceviewer.BuildProfile(records).Write(os.Stdout); err != nil {
+			return fmt.Errorf("failed to generate pprof: %v\n", err)
+		}
+		return nil
+	}
+
 	// Debug flags.
 	switch debug {
 	case 1: