Update use of MojoMediaLog without ThreadSafeAssociatedPtr

ThreadSafeAssociatedPtr is only supposed to be used by the IPC
conversion system.  In addition, it has a tendancy to post all
calls to MediaLog::AddEvent, which can have the side-effect of
ordering them after the (Mojo)VideoDecoder is destroyed since that
happens synchronously when VideoDecoder::Initialize fails.  So, we
don't get messages that describe why the failure happened, since
MojoVideoDecoderService has torn down the binding by then.

Instead, we make MojoMediaLog thread safe, and avoid the extra post
in the process.

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: I50fdb27c169c4b68222aa92f46c41a9ff23b4413
Reviewed-on: https://chromium-review.googlesource.com/1139080
Commit-Queue: Frank Liberato <liberato@chromium.org>
Reviewed-by: Dan Sanders <sandersd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575722}
3 files changed