Mac capture: Use SHARED_IMAGE_USAGE_MACOS_VIDEO_TOOLBOX

GpuMemoryBuffers from capture are backed by CVPixelBuffers, which
need to be specially annotated because their IOSurfaces will always
report IOSurfaceIsInUse as true. The MACOS_VIDEO_TOOLBOX usage flag
can be used to indicate that IOSurfaceIsInUse is not usable.

Bug: 1125879
Change-Id: I9cdcb57d6c47a8ac0aa5cd3bb120b7b91113a508
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2409215Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: ccameron <ccameron@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806561}

third_party/blink/renderer/platform/video_capture/video_capture_impl.cc

@@ -142,7 +142,8 @@ struct VideoCaptureImpl::BufferContext
     if (buffer_context->gmb_resources_->mailbox.IsZero()) {
       uint32_t usage =
           gpu::SHARED_IMAGE_USAGE_GLES2 | gpu::SHARED_IMAGE_USAGE_RASTER |
-          gpu::SHARED_IMAGE_USAGE_DISPLAY | gpu::SHARED_IMAGE_USAGE_SCANOUT;
+          gpu::SHARED_IMAGE_USAGE_DISPLAY | gpu::SHARED_IMAGE_USAGE_SCANOUT |
+          gpu::SHARED_IMAGE_USAGE_MACOS_VIDEO_TOOLBOX;
       buffer_context->gmb_resources_->mailbox = sii->CreateSharedImage(
           gpu_memory_buffer.get(),
           buffer_context->gpu_factories_->GpuMemoryBufferManager(),