Re-create devtools client upon browser restart

telemetry/telemetry/internal/backends/chrome/chrome_browser_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 logging
 import pprint
 import shlex
 import sys
 
 from telemetry.core import exceptions
@@ skipping 121 matching lines @@
       # and installed a root certificate.
       replay_args.append('--ignore-certificate-errors')
     return replay_args
 
   def HasBrowserFinishedLaunching(self):
     assert self._port, 'No DevTools port info available.'
     return devtools_client_backend.IsDevToolsAgentAvailable(
         self._port,
         self._browser_target, self)
 
-  def _InitDevtoolsClientBackend(self, remote_devtools_port=None):
-    """ Initiate the devtool client backend which allow browser connection
-    through browser' devtool.
+  def _WaitForBrowserToComeUp(self, remote_devtools_port=None):
+    """ Wait for browser to come up.

[achuithb, 2017/08/09 21:32:48]

Let's add a comment here saying that we're also creating the devtools client
backend. 

I'm not sure _WaitForBrowserToComeUp is still a good name for this function now
that it has this side effect of initing DevToolsClientBackend. I'm fine with
this, but Ned may have a suggestion for a better name.

[pfeldman, 2017/08/09 21:46:19]

I think it is fine for client creation to be a by product of the browser
startup, that's how we connect to it anyways. It is actually beneficial to have
this creation being an implementation detail rather than being explicitly
invoked. Unless we have reasons to believe that we will have 
_WaitForBrowserToComeUp with no connection in the future.

[achuithb, 2017/08/09 21:53:26]

Acknowledged.

Makes sense to me - let's see if Ned has an opinion.

 
     Args:
       remote_devtools_port: The remote devtools port, if
           any. Otherwise assumed to be the same as self._port.
     """
-    assert not self._devtools_client, (
-        'Devtool client backend cannot be init twice')
-    self._devtools_client = devtools_client_backend.DevToolsClientBackend(
-        self._port, self._browser_target,
-        remote_devtools_port or self._port, self)
-
-  def _WaitForBrowserToComeUp(self):
-    """ Wait for browser to come up. """
     try:
       timeout = self.browser_options.browser_startup_timeout
       py_utils.WaitFor(self.HasBrowserFinishedLaunching, timeout=timeout)
     except (py_utils.TimeoutException, exceptions.ProcessGoneException) as e:
       if not self.IsBrowserRunning():
         raise exceptions.BrowserGoneException(self.browser, e)
       raise exceptions.BrowserConnectionGoneException(self.browser, e)
+    self._devtools_client = devtools_client_backend.DevToolsClientBackend(
+        self._port, self._browser_target,
+        remote_devtools_port or self._port, self)
 
   def _WaitForExtensionsToLoad(self):
     """ Wait for all extensions to load.
     Be sure to check whether the browser_backend supports_extensions before
     calling this method.
     """
     assert self._supports_extensions
     assert self._devtools_client, (
         'Waiting for extensions required devtool client to be initiated first')
     try:
@@ skipping 129 matching lines @@
   def supports_cpu_metrics(self):
     return True
 
   @property
   def supports_memory_metrics(self):
     return True
 
   @property
   def supports_power_metrics(self):
     return True