Do a better job of lining up text with page text.

Bug:3085564
Bug:3196224
Bug:3321608

Remove Touch.getMaxScrollX(), which is incorrect for my
purpose, and is not used anywhere else.  Instead use the
layout to determine the maximum horizontal scroll of a
textfield.

Now that textareas use layers, scroll the layer's picture
in the UI thread for vertical movement.  When passing a
click to webcore, also pass a message to scroll the actual
textarea so the click will be in the correct place.

Lastly, do not override bringPointIntoView, which allows
moving the insertion handler beyond the edge of a field to
scroll it.  Instead, override requestRectangleOnScreen to
do nothing, since my actual goal is to prevent the TextView
from changing the scroll of the WebView, which is done by
webkit.

Requires a change to external/webkit.

Change-Id: Ib91907599b792287c373d3678cb04e0cb5e34471