FileVideoCaptureDevice: Regulate framerate without drifting

We currently rely on PostDelayedTask with a constant frame interval to get a specified frame rate.
This CL dynamically adapts the delay to PostDelayedTask to keep the frame rate in sync.

BUG=492189

Review URL: https://codereview.chromium.org/1162903004

Cr-Commit-Position: refs/heads/master@{#332827}
2 files changed