NSView cleanup for CoreAnimation

Make devtools place the contents view as a child of the devtools view,
so that the contents appears on top of the devtools.

Add instances of ScopedNSDisableScreenUpdates while adjusting views,
and replace some instances of [NSWindow disableScreenUpdatesUntilFlush]
with this more explicit mechanism.

BUG=245900

Review URL: https://codereview.chromium.org/171973004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252537 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252537
Blink roll r167558 - r167589

TBR=acolwell

Review URL: https://codereview.chromium.org/165993011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252538 0039d316-1c4b-4281-b951-d872f2087c98
Update .DEPS.git

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252539 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252539