make gm background colors 565 compatible

make gm background colors 565 compatible

Change a batch of GM tests to convert their background color
so that it is representable in 8888 and 565.

Enable portable text in those same tests to minimize platform
differences.

In a couple of bitmap tests, use portable typefaces instead of
choosing 'Times' which may or may not be available on the platform.

R=borenet@google.com

Review URL: https://codereview.chromium.org/1176243006