Telemetry: Fix scrolling tests on Windows.
Telemetry: Fix scrolling tests on Windows.

The http://twitter.com/katyperry page failed because the document.readyState was
stuck in "interactive" and never went to "complete".

The behavior after this CL matches what the scrolling test used to do before the
interaction refactoring (i.e., it didn't wait for the page to become "complete"
then either.

BUG=

Review URL: https://codereview.chromium.org/11532006

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@172340 0039d316-1c4b-4281-b951-d872f2087c98

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