Fix for extension binding race condition when evaluating JS.

tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py

Index: tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
diff --git a/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py b/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
index 9d72dc67dee46dde36bc63bdd5c6c86d14db4076..1d18f3153770f6bae5714039d52eb11c3ebf1c81 100644
--- a/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
+++ b/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
@@ -138,8 +138,22 @@ class ChromeBrowserBackend(browser_backend.BrowserBackend):
         if not e.extension_id in self._extension_dict_backend:
           return False
         extension_object = self._extension_dict_backend[e.extension_id]
-        res = extension_object.EvaluateJavaScript(
-            extension_ready_js % e.extension_id)
+        try:
+          res = extension_object.EvaluateJavaScript(
+              extension_ready_js % e.extension_id)
+        except exceptions.EvaluateException:
+          # If the inspected page is not ready, we will get an error
+          # when we evaluate a JS expression, but we can just keep polling
+          # until the page is ready (crbug.com/251913).
+          res = None
+
+        # TODO(tengs): We don't have full support for getting the Chrome

[achuithb, 2013/10/01 23:50:39]

Does this comment need to be updated? We neeed the workaround for chrome
regardless of version, right?

[Tim Song, 2013/10/02 00:01:20]

If we can get the Chrome version reliably before launch, we only have to reload
the page for chrome versions without the blink patch.

[achuithb, 2013/10/02 00:34:44]

Ah, ok, I was under the impression that the blink patch got reverted.

+        # version before launch, so for now we use a generic workaround to
+        # check for an extension binding bug in old versions of Chrome.
+        # See crbug.com/263162 for details.
+        if res and extension_object.EvaluateJavaScript(
+            'chrome.runtime == null'):
+          extension_object.Reload()
         if not res:
           return False
       return True