GitLab

Move InitializeOnCurrentThread down from WebGraphicsContext3DImpl to WebGraphicsContext3DCommandBufferImpl and WebGraphicsContext3DInProcessCommandBufferImpl

in preparation for dis-inheriting these classes

BUG=338338
TBR=darin@chromium.org

Review URL: https://codereview.chromium.org/609973002

Cr-Commit-Position: refs/heads/master@{#297362}