Refactor viz::BeginFrameArgs::BeginFrameArgsType

 * Refactor out static_cast in mojo StructTraits by defining EnumTraits
   for BeginFrameArgsType

 * Remove unused constant BEGIN_FRAME_ARGS_TYPE_MAX from BeginFrameArgsType
   enum

R=kylechar

Bug: 921635
Change-Id: I0dbc1564c7460388ed62342216193d07ffae9493
Reviewed-on: https://chromium-review.googlesource.com/c/1412622
Reviewed-by: kylechar <kylechar@chromium.org>
Reviewed-by: Ria Jiang <riajiang@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Céline O'Neil <celineo@google.com>
Cr-Commit-Position: refs/heads/master@{#623408}
5 files changed