Send initializeChildFrame from RenderFrameProxy instead of WebLocalFrame.

This is part 3 which removes setIsRemote.  WebRemoteFrame::initializeFromFrame now sends the initializeChildFrame message instead of setIsRemote.  WebLocalFrameImpl::m_isRemote isn't used anywhere, so it is also removed.

Part 1: https://codereview.chromium.org/591413004/
Part 2: https://codereview.chromium.org/592263002/

BUG=416102, 407160

Review URL: https://codereview.chromium.org/609633003

git-svn-id: svn://svn.chromium.org/blink/trunk@183088 bbb929c8-8fbe-4397-9dbb-9b2b20218538