Send initializeChildFrame from RenderFrameProxy instead of WebLocalFrame.

This will clean up the hack introduced in https://codereview.chromium.org/591503003/ to allow out-of-process iframes to paint.

This CL is part 1 of 3.  It adds an initializeFromFrame() to WebRemoteFrame to do the work that setIsRemote() used to do.  initializeFromFrame is intended for transferring relevant properties to a remote frame that is about to replace the current frame.  Because this is specific to a local-to-remote frame transition, this is done with a new method rather than in WebFrame::swap().

This will be followed by Chromium-side Part 2 (https://codereview.chromium.org/592263002) which will replace RenderFrameImpl::OnSwapOut's call to setIsRemote with a call to initializeFromFrame.  Another blink-side CL will then remove WebLocalFrame::setIsRemote.

BUG=416102, 407160

Review URL: https://codereview.chromium.org/591413004

git-svn-id: svn://svn.chromium.org/blink/trunk@182645 bbb929c8-8fbe-4397-9dbb-9b2b20218538