[Telemetry] Fix JavaScript interpolation in telemetry actions

telemetry/telemetry/internal/actions/media_action.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.
 
 """Common media action functions."""
 
 import logging
 
 from telemetry.internal.actions import page_action
 from telemetry.internal.actions import utils
+from telemetry.util import js_template
 
 import py_utils
 
 
 class MediaAction(page_action.PageAction):
   def WillRunAction(self, tab):
     """Loads the common media action JS code prior to running the action."""
     utils.InjectJavaScript(tab, 'media_action.js')
 
   def RunAction(self, tab):
     super(MediaAction, self).RunAction(tab)
 
   def WaitForEvent(self, tab, selector, event_name, timeout_in_seconds):
     """Halts media action until the selector's event is fired.
 
     Args:
       tab: The tab to check for event on.
       selector: Media element selector.
       event_name: Name of the event to check if fired or not.
       timeout_in_seconds: Timeout to check for event, throws an exception if
           not fired.
     """
     py_utils.WaitFor(
         lambda: self.HasEventCompletedOrError(tab, selector, event_name),
         timeout=timeout_in_seconds)
 
   def HasEventCompletedOrError(self, tab, selector, event_name):
-    # TODO(catapult:#3028): Fix interpolation of JavaScript values.
-    if tab.EvaluateJavaScript(
-        'window.__hasEventCompleted("%s", "%s");' % (selector, event_name)):
+    # TODO(catapult:#3028): Render in JavaScript method when supported by API.
+    code = js_template.Render(
+        'window.__hasEventCompleted({{ selector }}, {{ event_name }});',
+        selector=selector, event_name=event_name)
+    if tab.EvaluateJavaScript(code):
       return True
     error = tab.EvaluateJavaScript('window.__error')
     if error:
       logging.error('Detected media error while waiting for %s: %s', event_name,
                     error)
       return True
     return False