base

Rename some variable to make it clear what data is being stored.

The object that carries drawing data between WebViewCore and WebView
uses ambiguous variable names that do not fully convey the meaning
of the values.  This change updates those names to make it clear to
the reader what the intention of those values is.

Change-Id: I5a403d44881e1fad366f3ec9930ee59134eccd88