Move implementation of WebFrameImpl::executeCommand to Editor

This patch moves |WebFrameImpl::executeComamnd()| to |Editor| class to make
"web" as thin API layer and ease of maintenance.

This patch also get rid of |WebViewImpl::bubblingScroll|, which
becomes unused function as result of moving |WebFrameImpl::executeCommand()|.

BUG=n/a
TEST=n/a; no behavior changes

Review URL: https://codereview.chromium.org/337473010

git-svn-id: svn://svn.chromium.org/blink/trunk@177179 bbb929c8-8fbe-4397-9dbb-9b2b20218538