Add support for GetByExtensionId

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 049b0786d8534829381fd52cb638ab97fcd35c52..497ac73bcfdaf4e8ce4251237a9e45032255db75 100644
--- a/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
+++ b/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
@@ -160,26 +160,27 @@ class ChromeBrowserBackend(browser_backend.BrowserBackend):
       for e in self._extensions_to_load:
         if not e.extension_id in self.extension_backend:
           return False
-        extension_object = self.extension_backend[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
-        # 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
+        for extension_object in self.extension_backend[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
+          # 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
+
     if wait_for_extensions and self._supports_extensions:
       try:
         util.WaitFor(AllExtensionsLoaded, timeout=60)