[telemetry] Add support for requesting memory dumps via DevTools API

tools/telemetry/telemetry/internal/backends/chrome_inspector/tracing_backend.py

 # Copyright 2013 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
 import time
 
 from telemetry import decorators
 from telemetry.internal.backends.chrome_inspector import inspector_websocket
 from telemetry.internal.backends.chrome_inspector import websocket
 from telemetry.timeline import trace_data as trace_data_module
 
 
 class TracingUnsupportedException(Exception):
   pass
 
 
 class TracingTimeoutException(Exception):
   pass
 
 
 class TracingUnrecoverableException(Exception):
   pass
 
 
 class TracingHasNotRunException(Exception):
   pass
 
 
+class TracingUnexpectedResponseException(Exception):
+  pass
+
+
 class TracingBackend(object):
   def __init__(self, devtools_port):
     self._inspector_websocket = inspector_websocket.InspectorWebsocket()
     self._inspector_websocket.RegisterDomain(
         'Tracing', self._NotificationHandler)
 
     self._inspector_websocket.Connect(
         'ws://127.0.0.1:%i/devtools/browser' % devtools_port)
     self._trace_events = []
     self._is_tracing_running = False
@@ skipping 42 matching lines @@
       req = {'method': 'Tracing.end'}
       self._inspector_websocket.SendAndIgnoreResponse(req)
       # After Tracing.end, chrome browser will send asynchronous notifications
       # containing trace data. This is until Tracing.tracingComplete is sent,
       # which means there is no trace buffers pending flush.
       self._CollectTracingData(timeout)
     self._is_tracing_running = False
     trace_data_builder.AddEventsTo(
       trace_data_module.CHROME_TRACE_PART, self._trace_events)
 
+  def DumpMemory(self, timeout=30):
+    """Dumps memory.
+
+    Returns:
+      GUID of the generated dump if successful, None otherwise.
+
+    Raises:
+      TracingTimeoutException: If more than |timeout| seconds has passed
+      since the last time any data is received.
+      TracingUnrecoverableException: If there is a websocket error.
+      TracingUnexpectedResponseException: If the response contains an error
+      or does not contain the expected result.
+    """
+    request = {
+      'method': 'Tracing.requestMemoryDump'
+    }
+    try:
+      response = self._inspector_websocket.SyncRequest(request, timeout)
+    except websocket.WebSocketTimeoutException:
+      raise TracingTimeoutException
+    except (socket.error, websocket.WebSocketException,
+            inspector_websocket.WebSocketDisconnected):
+      raise TracingUnrecoverableException
+
+    if ('error' in response or
+        'result' not in response or
+        'success' not in response['result'] or
+        'dumpGuid' not in response['result']):
+      raise TracingUnexpectedResponseException(
+          'Inspector returned unexpected response for '
+          'Tracing.requestMemoryDump:\n' + json.dumps(response, indent=2))
+
+    result = response['result']
+    return result['dumpGuid'] if result['success'] else None
+
   def _CollectTracingData(self, timeout):
     """Collects tracing data. Assumes that Tracing.end has already been sent.
 
     Args:
       timeout: The timeout in seconds.
 
     Raises:
       TracingTimeoutException: If more than |timeout| seconds has passed
       since the last time any data is received.
       TracingUnrecoverableException: If there is a websocket error.
@@ skipping 33 matching lines @@
       return True
 
   def Close(self):
     self._inspector_websocket.Disconnect()
 
   @decorators.Cache
   def IsTracingSupported(self):
     req = {'method': 'Tracing.hasCompleted'}
     res = self._inspector_websocket.SyncRequest(req)
     return not res.get('response')