Reland r247589:<webview>: Fix text selection features in mac.

Reland r247589: <webview>: Fix text selection features in mac.

The suspected test flake (Shim_ScreenshotCapture) is not relevant. That test was also disabled in r247867.

> <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.
>
TBR=sky@chromium.org
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.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=249220

[lazyboy, 2014-02-05 19:46:38]

The CQ bit was checked by lazyboy@chromium.org

[commit-bot: I haz the power, 2014-02-05 19:59:43]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/lazyboy@chromium.org/149803008/1

[commit-bot: I haz the power, 2014-02-05 21:49:00]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-02-05 21:49:00]

Retried try job too often on win_rel for step(s) telemetry_perf_unittests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_rel&nu...

[lazyboy, 2014-02-05 21:54:14]

The CQ bit was checked by lazyboy@chromium.org

[commit-bot: I haz the power, 2014-02-05 22:00:12]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/lazyboy@chromium.org/149803008/1

[commit-bot: I haz the power, 2014-02-06 02:07:56]

Change committed as 249220