cc: Improve RasterWorkerPool perftests.

Adds a BuildRasterTaskQueue test and improves code coverage of existing
tests by making every other task required for activation. A regression
in test results is expected result of making the tests do more work.

BUG=269841
TEST=cc_perftests --gtest_filter=RasterWorkerPool*

Review URL: https://codereview.chromium.org/171423015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252818 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252818