telemetry: Added timeout parameter to StartTracing.

tools/telemetry/telemetry/core/chrome/browser_backend.py

Index: tools/telemetry/telemetry/core/chrome/browser_backend.py
diff --git a/tools/telemetry/telemetry/core/chrome/browser_backend.py b/tools/telemetry/telemetry/core/chrome/browser_backend.py
index 772fe28270d1619191b31db6247202e0242c3c91..5bb4e2a4b69ab369d6a8866555406e8103a8a69f 100644
--- a/tools/telemetry/telemetry/core/chrome/browser_backend.py
+++ b/tools/telemetry/telemetry/core/chrome/browser_backend.py
@@ -12,6 +12,7 @@ import sys
 from telemetry.core import util
 from telemetry.core import exceptions
 from telemetry.core import user_agent
+from telemetry.core import web_contents
 from telemetry.core import wpr_modes
 from telemetry.core import wpr_server
 from telemetry.core.chrome import extension_dict_backend
@@ -201,7 +202,8 @@ class BrowserBackend(object):
   def supports_tracing(self):
     return self.is_content_shell or self._chrome_branch_number >= 1385
 
-  def StartTracing(self, custom_categories=None):
+  def StartTracing(self, custom_categories=None,
+                   timeout=web_contents.DEFAULT_WEB_CONTENTS_TIMEOUT):
     """ custom_categories is an optional string containing a list of
     comma separated categories that will be traced instead of the
     default category set.  Example: use
@@ -210,7 +212,7 @@ class BrowserBackend(object):
     """
     if self._tracing_backend is None:
       self._tracing_backend = tracing_backend.TracingBackend(self._port)
-    self._tracing_backend.BeginTracing(custom_categories)
+    self._tracing_backend.BeginTracing(custom_categories, timeout)
 
   def StopTracing(self):
     self._tracing_backend.EndTracing()