Rename some functions of which names contain 'WebCore.'

- WebLocalFrameImpl::initializeWebCoreFrame
- WebLocalFrameImpl::setWebCoreFrame
- WebRemoteFrameImpl::initializeCoreFrame
- WebRemoteFrameImpl::setWebCoreFrame
- WebViewImpl::focusedCoreFrame
- toWebCoreFrame
- updateWebMouseEventFromWebCoreMouseEvent

BUG=none
TEST=none; no behavior changes.

Review URL: https://codereview.chromium.org/474143002

git-svn-id: svn://svn.chromium.org/blink/trunk@180337 bbb929c8-8fbe-4397-9dbb-9b2b20218538