Remove dead functions in Chrome and ChromeClient.

This CL removes the followings:

- Chrome::unfocus
  - ChromeClient::unfocus
   - ChromeClientImpl::unfocus
   - EmptyChromeClient::unfocus
- ScrollView::screenToContents
  - HostWindow::screenToRootView
    - Chrome::screenToRootView
      - ChromeClient::screenToRootView
        - ChromeClientImpl::screenToRootView
        - EmptyChromeClient::screenToRootView
      - WebPopupMenuImpl::screenToRootView
- RenderLayerCompositor::didChangeVisibleRect
  - ChromeClient::scheduleCompositingLayerFlush
    - ChromeClientImpl::scheduleCompositingLayerFlush
    - EmptyChromeClient::scheduleCompositingLayerFlush
- ChromeClient::openPagePopup and closePagePopup
  - EmptyChromeClient::openPagePopup and closePagePopup
  They are not called from WebCore. openPagePopup and closePagePopup of
  ChromeClientImpl should not be virtual.
- ChromeClient::isPointerLocked
  - ChromeClientImpl::isPointerLocked
- ChromeClient::isEmptyChromeClient
  - EmptyChromeClient::isEmptyChromeClient
- Chrome::layoutUpdated
- ChromeClient::allowsAcceleratedCompositing

BUG=none
TEST=none; no behavior changes.

Review URL: https://codereview.chromium.org/151193002

git-svn-id: svn://svn.chromium.org/blink/trunk@166282 bbb929c8-8fbe-4397-9dbb-9b2b20218538