Re-create devtools client upon browser restart

telemetry/telemetry/internal/backends/chrome/chrome_browser_backend.py

Index: telemetry/telemetry/internal/backends/chrome/chrome_browser_backend.py
diff --git a/telemetry/telemetry/internal/backends/chrome/chrome_browser_backend.py b/telemetry/telemetry/internal/backends/chrome/chrome_browser_backend.py
index 2133ca53af3a7e4c13c08e1e0477c0b3e4285132..f5b02fb12b6163871e6036e532abd7b115dd8024 100644
--- a/telemetry/telemetry/internal/backends/chrome/chrome_browser_backend.py
+++ b/telemetry/telemetry/internal/backends/chrome/chrome_browser_backend.py
@@ -139,22 +139,13 @@ class ChromeBrowserBackend(browser_backend.BrowserBackend):
         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)
@@ -162,6 +153,9 @@ class ChromeBrowserBackend(browser_backend.BrowserBackend):
       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.