Move forwardInputEvent to RemoteFrameClient.

This will eventually go away, but it doesn't belong on ChromeClient
in the meantime.

BUG=339659
TEST=No behavior change.

Review URL: https://codereview.chromium.org/642823006

git-svn-id: svn://svn.chromium.org/blink/trunk@183839 bbb929c8-8fbe-4397-9dbb-9b2b20218538