Removes leftover placeholder comment.

Removes line in VideoFrameResourceProvider indicating that it is a
placeholder class. This is now incorrect, as it has been filled in.

Bug: 746182
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: Id7be5af35c6ded2aca95e9721c33c961b171efc7
Reviewed-on: https://chromium-review.googlesource.com/1000524
Commit-Queue: CJ DiMeglio <lethalantidote@chromium.org>
Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549310}

third_party/blink/renderer/platform/graphics/video_frame_resource_provider.h

@@ -24,7 +24,6 @@ class SharedBitmapManager;
 
 namespace blink {
 
-// Placeholder class, to be implemented in full in later CL.
 // VideoFrameResourceProvider obtains required GPU resources for the video
 // frame.
 // VideoFrameResourceProvider methods are currently called on the media thread.