Fix the cause of AwZoomTest#testMagnification... tests flakiness

AwContents maintains its own page scale value, which it receives
synchronously from the compositor. However, it was still using page scale
limits values from ContentViewCore, where they are updated async-ly.
This was causing spurious wrong 'canZoomOut' results.

Fixed by propagating page scale limits to AwContents together with
page scale updates. It would be great to eliminate duplication of page
scale values between ContentViewCore and AwContents though.

Re-applied changes to the tests from https://codereview.chromium.org/143683005
as they still make sense.

BUG=340327,340648

Review URL: https://codereview.chromium.org/156233005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250706 0039d316-1c4b-4281-b951-d872f2087c98
Remove Mac AVFoundation experiment and enable AVFoundation by default.

This CL removes the code introduced to support a Chrome
Finch experiment, in the CL [1]. It also enables
AVFoundation by default, flipping the media switch
--enable-avfoundation with --disable-avfoundation.

[1] https://codereview.chromium.org/128373002/

BUG=158170,309554

Review URL: https://codereview.chromium.org/144473006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250707 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250707
Add GetDeviceSupportedFormats to Mac AVFoundation.

Add +getDevice:supportedFormats: to VideoCaptureDeviceAVFoundation.

Added GetDeviceSupportedFormats() to VideoCaptureDeviceMac that
simply multiplexes the QTKit/AVFoundation implementation. QtKit
remains NOTIMPLEMENTED(), AVFoundation version is written.

Three colorspaces are supported: YUYV, YUY2, MJPEG.

BUG=309554

Review URL: https://codereview.chromium.org/156553002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250708 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250708