Do not update, and return the previous matrix if surface_texture_ is null.

surface_texture_ should only be null during stub destruction; returning
the previous matrix will allow the last frame to be redrawn correctly.

BUG=614224
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_optional_gpu_tests_rel;tryserver.chromium.mac:mac_optional_gpu_tests_rel;tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2016643002
Cr-Commit-Position: refs/heads/master@{#396442}
1 file changed