Move PageConsole to using FrameHost instead of Page

This is not a complete move.  PageConsole still needs
to reach through FrameHost to Page to get the mainFrame
to get the main document to pass to the inspector.
But otherwise it only needs chrome() which is accessible
from FrameHost.

BUG=305811
R=abarth@chromium.org, abarth

Review URL: https://codereview.chromium.org/111113003

git-svn-id: svn://svn.chromium.org/blink/trunk@164146 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Devirtualize beginParsingChildren and move to Element

We don't actually need beginParsingChildren to be virtual since there
are no overrides. We also don't need begin or finishParsingChildren to
be on Node since the HTML parser never creates ProcessingInstructions
now and the XMLDocumentParser manages the processing instruction manually.

This means we should avoid the virtual calls for these for all Text nodes
and have half as many for Elements inside the parser as finishedParsingChildren
remains virtual.

Review URL: https://codereview.chromium.org/93623004

git-svn-id: svn://svn.chromium.org/blink/trunk@164147 bbb929c8-8fbe-4397-9dbb-9b2b20218538