Telemetry / Devtools TraceHandler: exposes tracing via dev tools.

tools/telemetry/telemetry/tracing_backend.py

Index: tools/telemetry/telemetry/tracing_backend.py
diff --git a/tools/telemetry/telemetry/tracing_backend.py b/tools/telemetry/telemetry/tracing_backend.py
new file mode 100644
index 0000000000000000000000000000000000000000..54f905782fa4812bbc9680782d8ec842cc71abc0
--- /dev/null
+++ b/tools/telemetry/telemetry/tracing_backend.py
@@ -0,0 +1,63 @@
+# 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.
+
+import json
+import logging
+import socket
+
+from telemetry import util
+from telemetry import websocket
+
+
+class TracingBackend(object):
+  def __init__(self, devtools_port):
+    debugger_url = 'ws://localhost:%i/devtools/browser' % devtools_port
+    self._socket = websocket.create_connection(debugger_url)
+    self._next_request_id = 0
+    self._cur_socket_timeout = 0
+
+  def BeginTracing(self):
+    req = {'method': 'Tracing.start'}
+    self._SyncRequest(req)
+
+  def EndTracingAsync(self):
+    req = {'method': 'Tracing.end'}
+    self._SyncRequest(req)
+
+  def HasCompleted(self):
+    req = {'method': 'Tracing.hasCompleted'}
+    r = self._SyncRequest(req)
+    return r['response']['result']
+
+  def GetTraceAndReset(self):
+    req = {'method': 'Tracing.getTraceAndReset'}
+    r = self._SyncRequest(req)
+    return '{"traceEvents":[' + r['response']['result'] + ']}'
+
+  def _SyncRequest(self, req, timeout=10):
+    self._SetTimeout(timeout)
+    req['id'] = self._next_request_id
+    self._next_request_id += 1
+    data = json.dumps(req)
+    logging.debug('will send [%s]', data)
+    self._socket.send(data)
+
+    while True:
+      try:
+        data = self._socket.recv()
+      except (socket.error, websocket.WebSocketException):
+        raise util.TimeoutException(
+            'Timed out waiting for reply. This is unusual.')
+
+      logging.debug('got [%s]', data)
+      res = json.loads(data)
+      if res['id'] != req['id']:
+        logging.debug('Dropped reply: %s', json.dumps(res))
+        continue
+      return res
+
+  def _SetTimeout(self, timeout):
+    if self._cur_socket_timeout != timeout:
+      self._socket.settimeout(timeout)
+      self._cur_socket_timeout = timeout