Do not update, and return the previous matrix if surface_texture_ is null.
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}
(cherry picked from commit 42b137d8600104c1853de10626f6ef1e15e972ab)

Review URL: https://codereview.chromium.org/2058613003 .

Cr-Commit-Position: 03d981dee550804c6934fd1a1d9cfa3c172affd3@{#312}
Cr-Branched-From: e9621a186760eb36d74098d9e33e4dd91c427b34@{#394939}

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