Fix build break in pyautolib with gcc >= 4.5.

chrome/test/pyautolib/pyauto.py

Index: chrome/test/pyautolib/pyauto.py
===================================================================
--- chrome/test/pyautolib/pyauto.py	(revision 84245)
+++ chrome/test/pyautolib/pyauto.py	(working copy)
@@ -534,7 +534,10 @@
     This is a snapshot of the bookmark model; it is not a proxy and
     does not get updated as the bookmark model changes.
     """
-    return bookmark_model.BookmarkModel(self._GetBookmarksAsJSON())
+    bookmarks_as_json = self._GetBookmarksAsJSON()
+    if bookmarks_as_json == None:
+      raise JSONInterfaceError('Could not resolve browser proxy.')
+    return bookmark_model.BookmarkModel(bookmarks_as_json)
 
   def GetDownloadsInfo(self, windex=0):
     """Return info about downloads.