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 "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 shell {
+
+Tracer::Tracer() : tracing_(false), blocks_written_(0u), trace_file_(nullptr) {
+}
+Tracer::~Tracer() {
+}
+
+void Tracer::Start(std::string categories) {
+  printf("tracing started\n");

[jamesr, 2015/04/07 20:33:56]

whoops, didn't mean to check these in. will delete. (maybe that presubmit is
useful?)

+  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(std::string filename) {
+  printf("tracing stopped\n");
+  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 (blocks_written_) {
+    fwrite(",", 1, 1, trace_file_);
+  }
+
+  ++blocks_written_;
+  fwrite(events_str->data().c_str(), 1, events_str->data().length(),
+         trace_file_);
+  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();

[jamesr, 2015/04/07 20:23:37]

if the message loop is running (i.e. we're stopping tracing due to the timeout
elapsing and not shutdown) then this really should spin a RunLoop to not freeze
up the thread. will fix in a follow-up

+  LOG(INFO) << "Wrote trace data to " << filename;
+}
+
+}  // namespace shell