Files.app: Split the test_case.js file.

Currently the test cases of Files.app's browser test are contained in the single
file. This CL split the huge file.

BUG=none
TEST=browser_tests
R=mtomasz@chromium.org

Review URL: https://codereview.chromium.org/168043005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252890 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252890
Automated Commit: Committing new LKGM version 5539.0.0 for chromeos.

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252891 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252891