Telemetry / Devtools TraceHandler: exposes tracing via dev tools.

content/browser/debugger/devtools_tracing_handler.cc

+// Copyright (c) 2012 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 "content/browser/debugger/devtools_tracing_handler.h"
+
+#include "base/bind.h"
+#include "base/callback.h"
+#include "base/location.h"
+#include "base/values.h"
+#include "content/browser/debugger/devtools_http_handler_impl.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/trace_controller.h"
+#include "content/public/browser/trace_subscriber.h"
+
+namespace content {
+
+DevToolsTracingHandler::DevToolsTracingHandler()
+    : has_completed_(false) {
+}
+
+DevToolsTracingHandler::~DevToolsTracingHandler() {
+}
+
+void DevToolsTracingHandler::OnEndTracingComplete() {
+  has_completed_ = true;
+}
+
+void DevToolsTracingHandler::OnTraceDataCollected(
+    const scoped_refptr<base::RefCountedString>& trace_fragment) {
+  buffer_.push_back(trace_fragment->data());
+}
+
+base::Value* DevToolsTracingHandler::OnProtocolCommand(
+    const std::string& method,
+    const base::DictionaryValue* params) {
+  if (method == "Tracing.start")
+    return Start(params);
+  else if (method == "Tracing.end")
+    return End(params);
+  else if (method == "Tracing.hasCompleted")
+    return HasCompleted(params);
+  else if (method == "Tracing.getTraceAndReset")
+    return GetTraceAndReset(params);
+  return NULL;
+}
+
+base::Value* DevToolsTracingHandler::Start(
+    const base::DictionaryValue* params) {
+  std::string categories;
+  if (params && params->HasKey("categories"))
+    params->GetString("categories", &categories);
+  TraceController::GetInstance()->BeginTracing(this, categories);
+
+  return base::Value::CreateBooleanValue(true);
+}
+
+base::Value* DevToolsTracingHandler::End(
+    const base::DictionaryValue* /* params */) {
+  TraceController::GetInstance()->EndTracingAsync(this);
+
+  return base::Value::CreateBooleanValue(true);
+}
+
+
+base::Value* DevToolsTracingHandler::HasCompleted(
+    const base::DictionaryValue* /* params */) {
+
+  return base::Value::CreateBooleanValue(has_completed_);
+}
+
+base::Value* DevToolsTracingHandler::GetTraceAndReset(
+    const base::DictionaryValue* /* params */) {
+  std::string ret;

[pfeldman, 2012/12/14 18:35:05]

Since you anyways use append with no pre-allocated full size, you do not save
much on allocations.

[bulach, 2012/12/14 19:53:39]

tracking the size and reserve'ing..

+  for (std::vector<std::string>::const_iterator i = buffer_.begin();
+       i != buffer_.end(); ++i) {
+    if (!ret.empty())
+      ret.append(",");
+    ret.append(*i);
+  }
+  buffer_.clear();
+  has_completed_ = false;
+
+  return base::Value::CreateStringValue(ret);
+}
+
+}  // namespace content