Don't include scroll offset in offsetFromLayoutObject for scrolling contents layers.

As a side-effect, this patch changes the system to no longer invalidate both the scrolling contents layer and m_graphicsLayer, since they now have different coordinate systems. (This has been a long-standing bug.)

BUG=529938,416535

Review-Url: https://codereview.chromium.org/2019583002
Cr-Commit-Position: refs/heads/master@{#396951}
22 files changed