scheduler: Rename WebPageScheduler to WebFrameHostScheduler

Rename the WebPageScheduler as WebFrameHostScheduler since we eventually
want to hang this object off of FrameHost instead of Page.

BUG=510398

Review URL: https://codereview.chromium.org/1348853002

git-svn-id: svn://svn.chromium.org/blink/trunk/public@202580 bbb929c8-8fbe-4397-9dbb-9b2b20218538
3 files changed