Add shell::Tracer object and wire up to --trace-startup on Android

shell/tracer.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "shell/tracer.h"
+
+#include <stdio.h>
+#include <string.h>
+
+#include "base/message_loop/message_loop.h"
+#include "base/synchronization/waitable_event.h"
+#include "base/threading/thread.h"
+#include "base/trace_event/trace_event.h"
+
+namespace mojo {
+namespace shell {
+
+Tracer::Tracer()
+    : tracing_(false), first_chunk_written_(false), trace_file_(nullptr) {
+}
+
+Tracer::~Tracer() {
+}
+
+void Tracer::Start(const std::string& categories) {
+  tracing_ = true;
+  base::trace_event::CategoryFilter category_filter(categories);
+  base::trace_event::TraceLog::GetInstance()->SetEnabled(
+      category_filter, base::trace_event::TraceLog::RECORDING_MODE,
+      base::trace_event::TraceOptions(base::trace_event::RECORD_UNTIL_FULL));
+}
+
+void Tracer::StopAndFlushToFile(const std::string& filename) {
+  if (tracing_)
+    StopTracingAndFlushToDisk(filename);
+}
+
+void Tracer::EndTraceAndFlush(const std::string& filename,
+                              const base::Closure& done_callback) {
+  trace_file_ = fopen(filename.c_str(), "w+");
+  PCHECK(trace_file_);
+  static const char kStart[] = "{\"traceEvents\":[";
+  fwrite(kStart, 1, strlen(kStart), trace_file_);
+  base::trace_event::TraceLog::GetInstance()->SetDisabled();
+  base::trace_event::TraceLog::GetInstance()->Flush(base::Bind(
+      &Tracer::WriteTraceDataCollected, base::Unretained(this), done_callback));
+}
+
+void Tracer::WriteTraceDataCollected(
+    const base::Closure& done_callback,
+    const scoped_refptr<base::RefCountedString>& events_str,
+    bool has_more_events) {
+  if (events_str->size()) {
+    if (!first_chunk_written_)
+      fwrite(",", 1, 1, trace_file_);
+
+    first_chunk_written_ = true;
+    fwrite(events_str->data().c_str(), 1, events_str->data().length(),
+           trace_file_);
+  } else
+    printf("got empty chunk, skipping. has_more_events %d\n", has_more_events);

[viettrungluu, 2015/04/08 00:39:15]

I don't think you really want this printf (and if you did, this else block would
need braces).

+
+  if (!has_more_events) {
+    static const char kEnd[] = "]}";
+    fwrite(kEnd, 1, strlen(kEnd), trace_file_);
+    PCHECK(fclose(trace_file_) == 0);
+    trace_file_ = nullptr;
+    done_callback.Run();
+  }
+}
+
+void Tracer::StopTracingAndFlushToDisk(const std::string& filename) {
+  tracing_ = false;
+  base::trace_event::TraceLog::GetInstance()->SetDisabled();
+  base::WaitableEvent flush_complete_event(false, false);
+  // TraceLog::Flush requires a message loop but we've already shut ours down.
+  // Spin up a new thread to flush things out.
+  base::Thread flush_thread("mojo_shell_trace_event_flush");
+  flush_thread.Start();
+  flush_thread.message_loop()->PostTask(
+      FROM_HERE,
+      base::Bind(&Tracer::EndTraceAndFlush, base::Unretained(this), filename,
+                 base::Bind(&base::WaitableEvent::Signal,
+                            base::Unretained(&flush_complete_event))));
+  flush_complete_event.Wait();
+  LOG(INFO) << "Wrote trace data to " << filename;
+}
+
+}  // namespace shell
+}  // namespace mojo