Revise history pyauto test to account for UI change.
Revise history pyauto test to account for UI change.

When the history page loads, its tab title is temporarily "Loading..."
until the page finishes loading all content.  This required a minor change
to a history test to account for that fact.

BUG=120043
TEST=Verified that the test used to fail, but now passes with these changes
     using --repeat=5 on my local linux machine.

Review URL: https://chromiumcodereview.appspot.com/9855002

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@128977 0039d316-1c4b-4281-b951-d872f2087c98

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