Snapshot a pointer to the main frame when creating WebViewFrameWidget.

Snapshot a pointer to the main frame when creating WebViewFrameWidget.

Otherwise, invoking WebViewFrameWidget::close() from frame swap will
result in trying to clear the frame widget on the wrong main frame.

Other miscellaneous fixes:
- WebViewFrameWidget now uses smart pointers where appropriate for its
  members.
- WebViewFrameWidget's ctor also takes a WebWidgetClient* pointer.
  This is future-proofing to help merge the widget implementations in
  WebFrameWidget and WebView.

BUG=419087
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=201048

[dcheng, 2015-08-22 05:40:43]

dcheng@chromium.org changed reviewers:
+ haraken@chromium.org

[dcheng, 2015-08-24 00:12:34]

This is needed to unblock progress on https://codereview.chromium.org/1303773002
as well.

[haraken, 2015-08-24 01:00:29]

LGTM

[dcheng, 2015-08-24 02:23:27]

The CQ bit was checked by dcheng@chromium.org

[commit-bot: I haz the power, 2015-08-24 02:23:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1310063002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1310063002/20001

[commit-bot: I haz the power, 2015-08-24 04:16:09]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=201048