Fix the flakiness issue in Telemetry tests.

+ Implement a more stable way to check if the dialog is fully loaded before choose the sink, instead of hardcoding the waiting time.

+ Also increase the timeout for stopping session.

Review-Url: https://codereview.chromium.org/2166433003
Cr-Commit-Position: refs/heads/master@{#406756}

chrome/test/media_router/telemetry/benchmarks/pagesets/media_router_page.py

@@ -91,6 +91,21 @@ class CastPage(page.Page):
     self._WaitForResult(action_runner, verify_func, error_message,
                         timeout=timeout)
 
+  def WaitUntilDialogLoaded(self, action_runner, tab):
+    """Waits until dialog is fully loaded."""
+
+    self._WaitForResult(
+        action_runner,
+        lambda: tab.EvaluateJavaScript(
+             '!!window.document.getElementById('
+             '"media-router-container") &&'
+             'window.document.getElementById('
+             '"media-router-container").sinksToShow_ &&'
+             'window.document.getElementById('
+             '"media-router-container").sinksToShow_.length'),
+        'The dialog is not fully loaded within 15s.',
+         timeout=15)
+
   def _WaitForResult(self, action_runner, verify_func, error_message,
                      timeout=5):
     """Waits until the function finishes or timeout."""

chrome/test/media_router/telemetry/benchmarks/pagesets/media_router_perf_pages.py

@@ -92,11 +92,10 @@ class CastFlingingPage(media_router_page.CastPage):
           lambda: len(action_runner.tab.browser.tabs) >= 2,
           'MR dialog never showed up.')
 
-      # Wait for 2s to make sure the dialog is fully loaded.
-      action_runner.Wait(2)
       for tab in action_runner.tab.browser.tabs:
         # Choose sink
         if tab.url == 'chrome://media-router/':
+          self.WaitUntilDialogLoaded(action_runner, tab)
           self.ChooseSink(tab, sink_name)
 
       self._WaitForResult(
@@ -121,7 +120,8 @@ class CastFlingingPage(media_router_page.CastPage):
           action_runner,
           'stopSession();',
           lambda: not action_runner.EvaluateJavaScript('currentSession'),
-          'Failed to stop session')
+          'Failed to stop session',
+          timeout=30)
 
 
 class CastMirroringPage(media_router_page.CastPage):
@@ -147,11 +147,10 @@ class CastMirroringPage(media_router_page.CastPage):
           lambda: len(action_runner.tab.browser.tabs) >= 2,
           'MR dialog never showed up.')
 
-      # Wait for 2s to make sure the dialog is fully loaded.
-      action_runner.Wait(2)
       for tab in action_runner.tab.browser.tabs:
         # Choose sink
         if tab.url == 'chrome://media-router/':
+          self.WaitUntilDialogLoaded(action_runner, tab)
           self.ChooseSink(tab, sink_name)
 
       # Wait for 5s to make sure the route is created.