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- Removes unnecessary registerTests()
- Breaks down CrExtensionBrowserTest to smaller sub-classes so test files are included as needed, instead of loading all test files in each TEST_F. (This reduced the generated .cc file from 25XX lines to 16XX lines).
- Allow (in the future) each sub-classes to specify a more specific browserPreload url instead of always loading the entire page.

Bug: 750842
Change-Id: I9e178728724f41c63e59b4edc81589b4366c9df9
Reviewed-on: https://chromium-review.googlesource.com/595188
Commit-Queue: Scott Chen <scottchen@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491847}