Overhaul tracing_ui to use XHR and new tracing_controller

content/browser/tracing/tracing_ui.cc

Index: content/browser/tracing/tracing_ui.cc
diff --git a/content/browser/tracing/tracing_ui.cc b/content/browser/tracing/tracing_ui.cc
index 0609e196eba7a62f4274077a7577a5aa340f8ce2..6e471c28a8418c09417ed323c65864298c7ba498 100644
--- a/content/browser/tracing/tracing_ui.cc
+++ b/content/browser/tracing/tracing_ui.cc
@@ -6,568 +6,144 @@
 
 #include <string>
 
+#include "base/base64.h"
 #include "base/bind.h"
 #include "base/bind_helpers.h"
-#include "base/command_line.h"
-#include "base/debug/trace_event.h"
 #include "base/file_util.h"
-#include "base/json/string_escape.h"
+#include "base/json/json_reader.h"
+#include "base/json/json_writer.h"
 #include "base/memory/scoped_ptr.h"
-#include "base/safe_numerics.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
-#include "base/strings/stringprintf.h"
-#include "base/strings/utf_string_conversions.h"
 #include "base/values.h"
 #include "content/public/browser/browser_thread.h"
-#include "content/public/browser/content_browser_client.h"
-#include "content/public/browser/render_view_host.h"
-#include "content/public/browser/trace_controller.h"
-#include "content/public/browser/trace_subscriber.h"
+#include "content/public/browser/tracing_controller.h"
 #include "content/public/browser/web_contents.h"
-#include "content/public/browser/web_contents_view.h"
 #include "content/public/browser/web_ui.h"
 #include "content/public/browser/web_ui_data_source.h"
-#include "content/public/browser/web_ui_message_handler.h"
 #include "content/public/common/url_constants.h"
 #include "grit/tracing_resources.h"
-#include "ipc/ipc_channel.h"
-#include "ui/shell_dialogs/select_file_dialog.h"
-
-#if defined(OS_CHROMEOS)
-#include "chromeos/dbus/dbus_thread_manager.h"
-#include "chromeos/dbus/debug_daemon_client.h"
-#endif
 
 namespace content {
 namespace {
 
-WebUIDataSource* CreateTracingHTMLSource() {
-  WebUIDataSource* source = WebUIDataSource::Create(kChromeUITracingHost);
-
-  source->SetJsonPath("strings.js");
-  source->SetDefaultResource(IDR_TRACING_HTML);
-  source->AddResourcePath("tracing.js", IDR_TRACING_JS);
-  return source;
-}
-
-// This class receives javascript messages from the renderer.
-// Note that the WebUI infrastructure runs on the UI thread, therefore all of
-// this class's methods are expected to run on the UI thread.
-class TracingMessageHandler
-    : public WebUIMessageHandler,
-      public ui::SelectFileDialog::Listener,
-      public base::SupportsWeakPtr<TracingMessageHandler>,
-      public TraceSubscriber {
- public:
-  TracingMessageHandler();
-  virtual ~TracingMessageHandler();
-
-  // WebUIMessageHandler implementation.
-  virtual void RegisterMessages() OVERRIDE;
-
-  // SelectFileDialog::Listener implementation
-  virtual void FileSelected(const base::FilePath& path,
-                            int index,
-                            void* params) OVERRIDE;
-  virtual void FileSelectionCanceled(void* params) OVERRIDE;
-
-  // TraceSubscriber implementation.
-  virtual void OnEndTracingComplete() OVERRIDE;
-  virtual void OnTraceDataCollected(
-      const scoped_refptr<base::RefCountedString>& trace_fragment) OVERRIDE;
-  virtual void OnTraceBufferPercentFullReply(float percent_full) OVERRIDE;
-  virtual void OnKnownCategoriesCollected(
-      const std::set<std::string>& known_categories) OVERRIDE;
-
-  // Messages.
-  void OnTracingControllerInitialized(const base::ListValue* list);
-  void OnBeginTracing(const base::ListValue* list);
-  void OnEndTracingAsync(const base::ListValue* list);
-  void OnBeginRequestBufferPercentFull(const base::ListValue* list);
-  void OnLoadTraceFile(const base::ListValue* list);
-  void OnSaveTraceFile(const base::ListValue* list);
-  void OnGetKnownCategories(const base::ListValue* list);
-
-  // Callbacks.
-  void LoadTraceFileComplete(string16* file_contents,
-                             const base::FilePath &path);
-  void SaveTraceFileComplete();
+void OnGotCategories(const WebUIDataSource::GotDataCallback& callback,
+                     const std::set<std::string>& categorySet) {
 
- private:
-  // The file dialog to select a file for loading or saving traces.
-  scoped_refptr<ui::SelectFileDialog> select_trace_file_dialog_;
-
-  // The type of the file dialog as the same one is used for loading or saving
-  // traces.
-  ui::SelectFileDialog::Type select_trace_file_dialog_type_;
-
-  // The trace data that is to be written to the file on saving.
-  scoped_ptr<std::string> trace_data_to_save_;
-
-  // True while tracing is active.
-  bool trace_enabled_;
-
-  // True while system tracing is active.
-  bool system_trace_in_progress_;
-
-  void OnEndSystemTracingAck(
-      const scoped_refptr<base::RefCountedString>& events_str_ptr);
-
-  DISALLOW_COPY_AND_ASSIGN(TracingMessageHandler);
-};
-
-// A proxy passed to the Read and Write tasks used when loading or saving trace
-// data.
-class TaskProxy : public base::RefCountedThreadSafe<TaskProxy> {
- public:
-  explicit TaskProxy(const base::WeakPtr<TracingMessageHandler>& handler)
-      : handler_(handler) {}
-  void LoadTraceFileCompleteProxy(string16* file_contents,
-                                  const base::FilePath& path) {
-    if (handler_.get())
-      handler_->LoadTraceFileComplete(file_contents, path);
-    delete file_contents;
-  }
-
-  void SaveTraceFileCompleteProxy() {
-    if (handler_.get())
-      handler_->SaveTraceFileComplete();
+  scoped_ptr<base::ListValue> category_list(new base::ListValue());
+  for (std::set<std::string>::const_iterator it = categorySet.begin();
+       it != categorySet.end(); it++) {
+    category_list->AppendString(*it);
   }
 
- private:
-  friend class base::RefCountedThreadSafe<TaskProxy>;
-  ~TaskProxy() {}
-
-  // The message handler to call callbacks on.
-  base::WeakPtr<TracingMessageHandler> handler_;
-
-  DISALLOW_COPY_AND_ASSIGN(TaskProxy);
-};
-
-////////////////////////////////////////////////////////////////////////////////
-//
-// TracingMessageHandler
-//
-////////////////////////////////////////////////////////////////////////////////
-
-TracingMessageHandler::TracingMessageHandler()
-    : select_trace_file_dialog_type_(ui::SelectFileDialog::SELECT_NONE),
-      trace_enabled_(false),
-      system_trace_in_progress_(false) {
+  base::RefCountedString* res = new base::RefCountedString();
+  base::JSONWriter::Write(category_list.get(), &res->data());
+  callback.Run(res);
 }
 
-TracingMessageHandler::~TracingMessageHandler() {
-  if (select_trace_file_dialog_.get())
-    select_trace_file_dialog_->ListenerDestroyed();
-
-  // If we are the current subscriber, this will result in ending tracing.
-  TraceController::GetInstance()->CancelSubscriber(this);
-
-  // Shutdown any system tracing too.
-    if (system_trace_in_progress_) {
-#if defined(OS_CHROMEOS)
-      chromeos::DBusThreadManager::Get()->GetDebugDaemonClient()->
-          RequestStopSystemTracing(
-              chromeos::DebugDaemonClient::EmptyStopSystemTracingCallback());
-#endif
-    }
-}
-
-void TracingMessageHandler::RegisterMessages() {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-
-  web_ui()->RegisterMessageCallback("tracingControllerInitialized",
-      base::Bind(&TracingMessageHandler::OnTracingControllerInitialized,
-                 base::Unretained(this)));
-  web_ui()->RegisterMessageCallback("beginTracing",
-      base::Bind(&TracingMessageHandler::OnBeginTracing,
-                 base::Unretained(this)));
-  web_ui()->RegisterMessageCallback("endTracingAsync",
-      base::Bind(&TracingMessageHandler::OnEndTracingAsync,
-                 base::Unretained(this)));
-  web_ui()->RegisterMessageCallback("beginRequestBufferPercentFull",
-      base::Bind(&TracingMessageHandler::OnBeginRequestBufferPercentFull,
-                 base::Unretained(this)));
-  web_ui()->RegisterMessageCallback("loadTraceFile",
-      base::Bind(&TracingMessageHandler::OnLoadTraceFile,
-                 base::Unretained(this)));
-  web_ui()->RegisterMessageCallback("saveTraceFile",
-      base::Bind(&TracingMessageHandler::OnSaveTraceFile,
-                 base::Unretained(this)));
-  web_ui()->RegisterMessageCallback("getKnownCategories",
-      base::Bind(&TracingMessageHandler::OnGetKnownCategories,
-                 base::Unretained(this)));
-}
-
-void TracingMessageHandler::OnTracingControllerInitialized(
-    const base::ListValue* args) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-
-  // Send the client info to the tracingController
-  {
-    scoped_ptr<base::DictionaryValue> dict(new base::DictionaryValue());
-    dict->SetString("version", GetContentClient()->GetProduct());
+void OnRecordingEnabledAck(const WebUIDataSource::GotDataCallback& callback);
 
-    dict->SetString("command_line",
-        CommandLine::ForCurrentProcess()->GetCommandLineString());
-
-    web_ui()->CallJavascriptFunction("tracingController.onClientInfoUpdate",
-                                     *dict);
+bool OnBeginRecording(const std::string& data64,
+                      const WebUIDataSource::GotDataCallback& callback) {
+  std::string data;
+  if (!base::Base64Decode(data64, &data)) {
+    LOG(ERROR) << "Options were not base64 encoded.";
+    return false;
   }
-}
-
-void TracingMessageHandler::OnBeginRequestBufferPercentFull(
-    const base::ListValue* list) {
-  TraceController::GetInstance()->GetTraceBufferPercentFullAsync(this);
-}
-
-// A callback used for asynchronously reading a file to a string. Calls the
-// TaskProxy callback when reading is complete.
-void ReadTraceFileCallback(TaskProxy* proxy, const base::FilePath& path) {
-  std::string file_contents;
-  if (!base::ReadFileToString(path, &file_contents))
-    return;
 
-  // We need to escape the file contents, because it will go into a javascript
-  // quoted string in TracingMessageHandler::LoadTraceFileComplete. We need to
-  // escape control characters (to have well-formed javascript statements), as
-  // well as \ and ' (the only special characters in a ''-quoted string).
-  // Do the escaping on this thread, it may take a little while for big files
-  // and we don't want to block the UI during that time. Also do the UTF-16
-  // conversion here.
-  // Note: we're using UTF-16 because we'll need to cut the string into slices
-  // to give to Javascript, and it's easier to cut than UTF-8 (since JS strings
-  // are arrays of 16-bit values, UCS-2 really, whereas we can't cut inside of a
-  // multibyte UTF-8 codepoint).
-  size_t size = file_contents.size();
-  std::string escaped_contents;
-  escaped_contents.reserve(size);
-  for (size_t i = 0; i < size; ++i) {
-    char c = file_contents[i];
-    if (c < ' ' || c == 0x7f) {
-      escaped_contents += base::StringPrintf("\\u%04x",
-                                             static_cast<uint8_t>(c));
-      continue;
-    }
-    if (c == '\\' || c == '\'')
-      escaped_contents.push_back('\\');
-    escaped_contents.push_back(c);
+  scoped_ptr<base::Value> optionsRaw(base::JSONReader::Read(data));
+  if (!optionsRaw) {
+    LOG(ERROR) << "Options were not valid JSON";
+    return false;
   }
-  file_contents.clear();
-
-  scoped_ptr<string16> contents16(new string16);
-  UTF8ToUTF16(escaped_contents).swap(*contents16);
-
-  BrowserThread::PostTask(
-      BrowserThread::UI, FROM_HERE,
-      base::Bind(&TaskProxy::LoadTraceFileCompleteProxy, proxy,
-                 contents16.release(),
-                 path));
-}
-
-// A callback used for asynchronously writing a file from a string. Calls the
-// TaskProxy callback when writing is complete.
-void WriteTraceFileCallback(TaskProxy* proxy,
-                            const base::FilePath& path,
-                            std::string* contents) {
-  int size = base::checked_numeric_cast<int>(contents->size());
-  if (file_util::WriteFile(path, contents->c_str(), size) != size)
-    return;
-
-  BrowserThread::PostTask(
-      BrowserThread::UI, FROM_HERE,
-      base::Bind(&TaskProxy::SaveTraceFileCompleteProxy, proxy));
-}
-
-void TracingMessageHandler::FileSelected(
-    const base::FilePath& path, int index, void* params) {
-  if (select_trace_file_dialog_type_ ==
-      ui::SelectFileDialog::SELECT_OPEN_FILE) {
-    BrowserThread::PostTask(
-        BrowserThread::FILE, FROM_HERE,
-        base::Bind(&ReadTraceFileCallback,
-                   make_scoped_refptr(new TaskProxy(AsWeakPtr())), path));
-  } else {
-    BrowserThread::PostTask(
-        BrowserThread::FILE, FROM_HERE,
-        base::Bind(&WriteTraceFileCallback,
-                   make_scoped_refptr(new TaskProxy(AsWeakPtr())), path,
-                   trace_data_to_save_.release()));
+  base::DictionaryValue* options;
+  if (!optionsRaw->GetAsDictionary(&options)) {
+    LOG(ERROR) << "Options must be dict";
+    return false;
   }
 
-  select_trace_file_dialog_ = NULL;
-}
-
-void TracingMessageHandler::FileSelectionCanceled(void* params) {
-  select_trace_file_dialog_ = NULL;
-  if (select_trace_file_dialog_type_ ==
-      ui::SelectFileDialog::SELECT_OPEN_FILE) {
-    web_ui()->CallJavascriptFunction(
-        "tracingController.onLoadTraceFileCanceled");
-  } else {
-    web_ui()->CallJavascriptFunction(
-        "tracingController.onSaveTraceFileCanceled");
+  std::string category_filter_string;
+  bool use_system_tracing;
+  bool use_continuous_tracing;
+  bool use_sampling;
+
+  bool options_ok = true;
+  options_ok &= options->GetString("categoryFilter", &category_filter_string);
+  options_ok &= options->GetBoolean("useSystemTracing", &use_system_tracing);
+  options_ok &= options->GetBoolean("useContinuousTracing",
+                                    &use_continuous_tracing);
+  options_ok &= options->GetBoolean("useSampling", &use_sampling);
+  if (!options_ok) {
+    LOG(ERROR) << "Malformed options";
+    return false;
   }
-}
-
-void TracingMessageHandler::OnLoadTraceFile(const base::ListValue* list) {
-  // Only allow a single dialog at a time.
-  if (select_trace_file_dialog_.get())
-    return;
-  select_trace_file_dialog_type_ = ui::SelectFileDialog::SELECT_OPEN_FILE;
-  select_trace_file_dialog_ = ui::SelectFileDialog::Create(
-      this,
-      GetContentClient()->browser()->CreateSelectFilePolicy(
-          web_ui()->GetWebContents()));
-  select_trace_file_dialog_->SelectFile(
-      ui::SelectFileDialog::SELECT_OPEN_FILE,
-      string16(),
-      base::FilePath(),
-      NULL,
-      0,
-      base::FilePath::StringType(),
-      web_ui()->GetWebContents()->GetView()->GetTopLevelNativeWindow(),
-      NULL);
-}
 
-void TracingMessageHandler::LoadTraceFileComplete(string16* contents,
-                                                  const base::FilePath& path) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  int tracing_options = 0;
+  if (use_system_tracing)
+    tracing_options |= TracingController::ENABLE_SYSTRACE;
+  if (use_sampling)
+    tracing_options |= TracingController::ENABLE_SAMPLING;
+  if (use_continuous_tracing)
+    tracing_options |= TracingController::RECORD_CONTINUOUSLY;
 
-  // We need to pass contents to tracingController.onLoadTraceFileComplete, but
-  // that may be arbitrarily big, and IPCs messages are limited in size. So we
-  // need to cut it into pieces and rebuild the string in Javascript.
-  // |contents| has already been escaped in ReadTraceFileCallback, so we need to
-  // avoid splitting escape sequences (e.g., \' or \u1234) to keep the data
-  // intact. IPC::Channel::kMaximumMessageSize is in bytes, and we need to
-  // account for overhead.
-  const size_t kMaxSize = IPC::Channel::kMaximumMessageSize / 2 - 128;
-  const size_t kControlCharEscapeSequenceSize = 5;
-  string16 first_prefix = UTF8ToUTF16("window.traceData = '");
-  string16 prefix = UTF8ToUTF16("window.traceData += '");
-  string16 suffix = UTF8ToUTF16("';");
-
-  RenderViewHost* rvh = web_ui()->GetWebContents()->GetRenderViewHost();
-
-  size_t flush_offset = 0;
-  size_t token_start = 0;
-  while (flush_offset < contents->size()) {
-    size_t token_end = token_start;
-    if ((*contents)[token_end] == '\\') {
-      token_end++;
-      DCHECK(token_end < contents->size());
-      if (token_end < contents->size() && (*contents)[token_end] == 'u') {
-        token_end += kControlCharEscapeSequenceSize;
-      } else {
-        token_end++;
-      }
-    } else {
-      token_end++;
-    }
-    token_end = std::min(contents->size(), token_end);
-    size_t token_size = token_end - token_start;
-    size_t flush_size = token_start - flush_offset;
-    if (token_end == contents->size()) {
-      flush_size = contents->size() - flush_offset;
-    } else if (flush_size + token_size < kMaxSize) {
-      token_start += token_size;
-      continue;
-    }
-    string16 javascript = flush_offset == 0 ? first_prefix : prefix;
-    javascript += contents->substr(flush_offset, flush_size) + suffix;
-    rvh->ExecuteJavascriptInWebFrame(string16(), javascript);
-    flush_offset += flush_size;
-  }
-
-  // The CallJavascriptFunction is not used because we need to pass
-  // the first param |window.traceData| through as an un-quoted string.
-  rvh->ExecuteJavascriptInWebFrame(string16(), UTF8ToUTF16(
-      "tracingController.onLoadTraceFileComplete(window.traceData," +
-      base::GetDoubleQuotedJson(path.value()) + ");" +
-      "delete window.traceData;"));
+  base::debug::CategoryFilter category_filter(category_filter_string);
+  return TracingController::GetInstance()->EnableRecording(
+      category_filter,
+      static_cast<TracingController::Options>(tracing_options),
+      base::Bind(OnRecordingEnabledAck, callback));
 }
 
-void TracingMessageHandler::OnSaveTraceFile(const base::ListValue* list) {
-  // Only allow a single dialog at a time.
-  if (select_trace_file_dialog_.get())
-    return;
-
-  DCHECK_EQ(1U, list->GetSize());
-
-  std::string* trace_data = new std::string();
-  bool ok = list->GetString(0, trace_data);
-  DCHECK(ok);
-  trace_data_to_save_.reset(trace_data);
-
-  select_trace_file_dialog_type_ = ui::SelectFileDialog::SELECT_SAVEAS_FILE;
-  select_trace_file_dialog_ = ui::SelectFileDialog::Create(
-      this,
-      GetContentClient()->browser()->CreateSelectFilePolicy(
-          web_ui()->GetWebContents()));
-  select_trace_file_dialog_->SelectFile(
-      ui::SelectFileDialog::SELECT_SAVEAS_FILE,
-      string16(),
-      base::FilePath(),
-      NULL,
-      0,
-      base::FilePath::StringType(),
-      web_ui()->GetWebContents()->GetView()->GetTopLevelNativeWindow(),
-      NULL);
+void OnRecordingEnabledAck(const WebUIDataSource::GotDataCallback& callback) {
+  base::RefCountedString* res = new base::RefCountedString();
+  callback.Run(res);
 }
 
-void TracingMessageHandler::SaveTraceFileComplete() {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  web_ui()->CallJavascriptFunction("tracingController.onSaveTraceFileComplete");
+void OnTraceBufferPercentFullResult(
+    const WebUIDataSource::GotDataCallback& callback, float result) {
+  std::string str = base::DoubleToString(result);
+  callback.Run(base::RefCountedString::TakeString(&str));
 }
 
-void TracingMessageHandler::OnBeginTracing(const base::ListValue* args) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  DCHECK_GE(args->GetSize(), (size_t) 2);
-  DCHECK_LE(args->GetSize(), (size_t) 3);
-
-  bool system_tracing_requested = false;
-  bool ok = args->GetBoolean(0, &system_tracing_requested);
-  DCHECK(ok);
-
-  std::string chrome_categories;
-  ok = args->GetString(1, &chrome_categories);
-  DCHECK(ok);
-
-  base::debug::TraceLog::Options options =
-      base::debug::TraceLog::RECORD_UNTIL_FULL;
-  if (args->GetSize() >= 3) {
-    std::string options_;
-    ok = args->GetString(2, &options_);
-    DCHECK(ok);
-    options = base::debug::TraceLog::TraceOptionsFromString(options_);
-  }
-
-  trace_enabled_ = true;
-  // TODO(jbates) This may fail, but that's OK for current use cases.
-  //              Ex: Multiple about:gpu traces can not trace simultaneously.
-  // TODO(nduca) send feedback to javascript about whether or not BeginTracing
-  //             was successful.
-  TraceController::GetInstance()->BeginTracing(this, chrome_categories,
-                                               options);
-
-  if (system_tracing_requested) {
-#if defined(OS_CHROMEOS)
-    DCHECK(!system_trace_in_progress_);
-    chromeos::DBusThreadManager::Get()->GetDebugDaemonClient()->
-        StartSystemTracing();
-    // TODO(sleffler) async, could wait for completion
-    system_trace_in_progress_ = true;
-#endif
-  }
+void ReadRecordingResult(const WebUIDataSource::GotDataCallback& callback,
+                         const base::FilePath& path) {
+  std::string tmp;
+  if (!base::ReadFileToString(path, &tmp))
+    LOG(ERROR) << "Failed to read file " << path.value();
+  base::DeleteFile(path, false);
+  callback.Run(base::RefCountedString::TakeString(&tmp));
 }
 
-void TracingMessageHandler::OnEndTracingAsync(const base::ListValue* list) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-
-  // This is really us beginning to end tracing, rather than tracing being truly
-  // over. When this function yields, we expect to get some number of
-  // OnTraceDataCollected callbacks, which will append data to window.traceData.
-  // To set up for this, set window.traceData to the empty string.
-  web_ui()->GetWebContents()->GetRenderViewHost()->
-    ExecuteJavascriptInWebFrame(string16(),
-                                UTF8ToUTF16("window.traceData = '';"));
-
-  // TODO(nduca): fix javascript code to make sure trace_enabled_ is always true
-  //              here. triggered a false condition by just clicking stop
-  //              trace a few times when it was going slow, and maybe switching
-  //              between tabs.
-  if (trace_enabled_ &&
-      !TraceController::GetInstance()->EndTracingAsync(this)) {
-    // Set to false now, since it turns out we never were the trace subscriber.
-    OnEndTracingComplete();
-  }
+void BeginReadingRecordingResult(
+    const WebUIDataSource::GotDataCallback& callback,
+    const base::FilePath& path) {
+  BrowserThread::PostTask(
+      BrowserThread::FILE, FROM_HERE,
+      base::Bind(ReadRecordingResult, callback, path));
 }
 
-void TracingMessageHandler::OnEndTracingComplete() {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  trace_enabled_ = false;
-  if (system_trace_in_progress_) {
-    // Disable system tracing now that the local trace has shutdown.
-    // This must be done last because we potentially need to push event
-    // records into the system event log for synchronizing system event
-    // timestamps with chrome event timestamps--and since the system event
-    // log is a ring-buffer (on linux) adding them at the end is the only
-    // way we're confident we'll have them in the final result.
-    system_trace_in_progress_ = false;
-#if defined(OS_CHROMEOS)
-    chromeos::DBusThreadManager::Get()->GetDebugDaemonClient()->
-        RequestStopSystemTracing(
-            base::Bind(&TracingMessageHandler::OnEndSystemTracingAck,
-            base::Unretained(this)));
-    return;
-#endif
+bool OnBeginRequest(const std::string& path,
+                    const WebUIDataSource::GotDataCallback& callback) {
+  if (path == "json/categories") {
+    TracingController::GetInstance()->GetCategories(
+        base::Bind(OnGotCategories, callback));
+    return true;
   }
-
-  RenderViewHost* rvh = web_ui()->GetWebContents()->GetRenderViewHost();
-  rvh->ExecuteJavascriptInWebFrame(string16(), UTF8ToUTF16(
-      "tracingController.onEndTracingComplete(window.traceData);"
-      "delete window.traceData;"));
-}
-
-void TracingMessageHandler::OnEndSystemTracingAck(
-    const scoped_refptr<base::RefCountedString>& events_str_ptr) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-
-  web_ui()->CallJavascriptFunction(
-      "tracingController.onSystemTraceDataCollected",
-      *scoped_ptr<base::Value>(new base::StringValue(events_str_ptr->data())));
-  DCHECK(!system_trace_in_progress_);
-
-  OnEndTracingComplete();
-}
-
-void TracingMessageHandler::OnTraceDataCollected(
-    const scoped_refptr<base::RefCountedString>& trace_fragment) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-
-  std::string javascript;
-  javascript.reserve(trace_fragment->size() * 2);
-  javascript.append("window.traceData += \"");
-  base::JsonDoubleQuote(trace_fragment->data(), false, &javascript);
-
-  // Intentionally append a , to the traceData. This technically causes all
-  // traceData that we pass back to JS to end with a comma, but that is actually
-  // something the JS side strips away anyway
-  javascript.append(",\";");
-
-  web_ui()->GetWebContents()->GetRenderViewHost()->
-    ExecuteJavascriptInWebFrame(string16(), UTF8ToUTF16(javascript));
-}
-
-void TracingMessageHandler::OnTraceBufferPercentFullReply(float percent_full) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  web_ui()->CallJavascriptFunction(
-      "tracingController.onRequestBufferPercentFullComplete",
-      *scoped_ptr<base::Value>(new base::FundamentalValue(percent_full)));
-}
-
-void TracingMessageHandler::OnGetKnownCategories(const base::ListValue* list) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  if (!TraceController::GetInstance()->GetKnownCategoryGroupsAsync(this)) {
-    std::set<std::string> ret;
-    OnKnownCategoriesCollected(ret);
+  const char* beginRecordingPath = "json/begin_recording?";
+  if (path.find(beginRecordingPath) == 0) {
+    std::string data = path.substr(strlen(beginRecordingPath));
+    return OnBeginRecording(data, callback);
   }
-}
-
-void TracingMessageHandler::OnKnownCategoriesCollected(
-    const std::set<std::string>& known_categories) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-
-  scoped_ptr<base::ListValue> categories(new base::ListValue());
-  for (std::set<std::string>::const_iterator iter = known_categories.begin();
-       iter != known_categories.end();
-       ++iter) {
-    categories->AppendString(*iter);
+  if (path == "json/get_buffer_percent_full") {
+    return TracingController::GetInstance()->GetTraceBufferPercentFull(
+        base::Bind(OnTraceBufferPercentFullResult, callback));
   }
-
-  web_ui()->CallJavascriptFunction(
-      "tracingController.onKnownCategoriesCollected", *categories);
+  if (path == "json/end_recording") {
+    return TracingController::GetInstance()->DisableRecording(
+        base::FilePath(), base::Bind(BeginReadingRecordingResult, callback));
+  }
+  if (StartsWithASCII(path, "json/", true))
+    LOG(ERROR) << "Unhandled request to " << path;
+  return false;
 }
 
 }  // namespace
@@ -580,12 +156,16 @@ void TracingMessageHandler::OnKnownCategoriesCollected(
 ////////////////////////////////////////////////////////////////////////////////
 
 TracingUI::TracingUI(WebUI* web_ui) : WebUIController(web_ui) {
-  web_ui->AddMessageHandler(new TracingMessageHandler());
-
   // Set up the chrome://tracing/ source.
   BrowserContext* browser_context =
       web_ui->GetWebContents()->GetBrowserContext();
-  WebUIDataSource::Add(browser_context, CreateTracingHTMLSource());
+
+  WebUIDataSource* source = WebUIDataSource::Create(kChromeUITracingHost);
+  source->SetJsonPath("strings.js");
+  source->SetDefaultResource(IDR_TRACING_HTML);
+  source->AddResourcePath("tracing.js", IDR_TRACING_JS);
+  source->SetRequestFilter(base::Bind(OnBeginRequest));
+  WebUIDataSource::Add(browser_context, source);
 }
 
 }  // namespace content