Mac: Fix Korean input on OSX 10.11
handling_input_event_ needs to be set in RenderWidget::OnImeSetComposition,
otherwise RenderView::DidChangeSelection will skip sending the selection
change message the the browser, even though it was correctly set on the
renderer side.
Also fix incorrectly set selectedRange_ in -setMarkedText,
|newSelRange| is relative to the marked text while selectedRange_ is
relative to the entire text storage.
BUG=500376
Review URL: https://codereview.chromium.org/
1240943002
Cr-Commit-Position: refs/heads/master@{#339754}