[Telemetry] Fix JavaScript interpolation in telemetry actions

telemetry/telemetry/internal/actions/media_action.py

Index: telemetry/telemetry/internal/actions/media_action.py
diff --git a/telemetry/telemetry/internal/actions/media_action.py b/telemetry/telemetry/internal/actions/media_action.py
index 6ae7ac3a4059a0a2be83dab711979577074e8fb0..3c53883c1b6d584d1633439fc7b003f539a685ff 100644
--- a/telemetry/telemetry/internal/actions/media_action.py
+++ b/telemetry/telemetry/internal/actions/media_action.py
@@ -8,6 +8,7 @@ import logging
 
 from telemetry.internal.actions import page_action
 from telemetry.internal.actions import utils
+from telemetry.util import js_template
 
 import py_utils
 
@@ -35,9 +36,11 @@ class MediaAction(page_action.PageAction):
         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: