Move m_containsPlugins from FrameLoader to Document

It's a property of the Document, not the Frame, and should never persist through
navigation.

BUG=none

Review URL: https://codereview.chromium.org/48283003

git-svn-id: svn://svn.chromium.org/blink/trunk@161207 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Move RTCConfiguration to platform/

BUG=297477

Review URL: https://codereview.chromium.org/54623004

git-svn-id: svn://svn.chromium.org/blink/trunk@161208 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Rename TextTrackRegion/TextTrackRegionList to VTTRegion/VTTRegionList

http://dev.w3.org/html5/webvtt/#vttregion-interface
http://dev.w3.org/html5/webvtt/#vttregionlist-interface

This is a completely mechanical rename, except for added instanceof
tests and removing NoInterfaceObject (not per spec) from VTTRegionList
to make them pass.

Silvia (the spec editor) says in the bug that the spec hasn't changed
since the implementation, so together with the fact that this is
RuntimeEnabled, it should be safe despite being Web facing.

BUG=313604

Review URL: https://codereview.chromium.org/55653003

git-svn-id: svn://svn.chromium.org/blink/trunk@161209 bbb929c8-8fbe-4397-9dbb-9b2b20218538