Revert 247589 "<webview>: Fix text selection features in mac."

> <webview>: Fix text selection features in mac.
> We still need to pass RWHVGuest::SelectionChanged() call to platform_view_.
> This broke while adding IME support, this function doesn't seem to be required for IME (made sure by running BrowserPluginHostTest.InputMethod).
> 
> Wrote a browser_test to catch the regression.
> 
> BUG=331722
> Test=Open a <webview> in a chrome app. Select some text. Observe that "Look up in dictionary" and "Speech=>Start Speaking" features work.
> 
> Review URL: https://codereview.chromium.org/148433007

Suspected of causing flakes in

WithoutThreadedCompositor/WebViewCaptureTest.Shim_ScreenshotCapture , see

http://build.chromium.org/p/chromium.webkit/builders/Mac10.8%20Tests/builds/5692
and
http://build.chromium.org/p/chromium.webkit/builders/Win7%20Tests/builds/928

TBR=lazyboy@chromium.org

Review URL: https://codereview.chromium.org/139803004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247722 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247722