[telemetry] Add TraceResult as return value from tracing, and placeholder trace_event_importer.

tools/telemetry/telemetry/browser.py

 # 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 os
 
 from telemetry import browser_credentials
 from telemetry import tab_list
 from telemetry import temporary_http_server
 from telemetry import wpr_modes
 from telemetry import wpr_server
@@ skipping 48 matching lines @@
   @property
   def supports_tracing(self):
     return self._browser_backend.supports_tracing
 
   def StartTracing(self):
     return self._browser_backend.StartTracing()
 
   def StopTracing(self):
     return self._browser_backend.StopTracing()
 
-  def GetTrace(self):
-    return self._browser_backend.GetTrace()
+  def GetTraceResultAndReset(self):
+    """Returns the result of the trace, as TraceResult object."""
+    return self._browser_backend.GetTraceResultAndReset()
 
   def Close(self):
     """Closes this browser."""
     if self._wpr_server:
       self._wpr_server.Close()
       self._wpr_server = None
 
     if self._http_server:
       self._http_server.Close()
       self._http_server = None
@@ skipping 43 matching lines @@
         archive_path,
         use_record_mode,
         self._browser_backend.WEBPAGEREPLAY_HOST,
         self._browser_backend.webpagereplay_local_http_port,
         self._browser_backend.webpagereplay_local_https_port,
         self._browser_backend.webpagereplay_remote_http_port,
         self._browser_backend.webpagereplay_remote_https_port)
 
   def GetStandardOutput(self):
     return self._browser_backend.GetStandardOutput()