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As a good citizen, not only write a unit test for the new function,
but also for the exsisting similar functions lacking unit tests.

BUG=135328
TEST=out/Release/unit_tests --gtest_filter=GDataCacheTest.GetResourceIdsOf*

Review URL: https://chromiumcodereview.appspot.com/10834052

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@148774 0039d316-1c4b-4281-b951-d872f2087c98