drm_hwcomposer: Add test_only mode to CommitFrame

Allow the caller of CommitFrame to run the commit in "test only" mode
which will send the frame to the kernel, but won't actually change any
registers.

Bug: 25379136
Test: Tested on smaug

Change-Id: I831b5f17d433bc60d9f107689feb1d7672c100a9
Signed-off-by: Sean Paul <seanpaul@chromium.org>
2 files changed