Fix a crash on WebViewFocusHelper destruction.

Fix a crash on WebViewFocusHelper destruction.

Remove WebViewFocusHelper; r287082 had object lifetime issues.

Fix Issue 368691 with a WebDialogWebContentsDelegate instead:
Remove CreateConstrainedWebDialog's |tab_delegate| parameter.
Delete the custom PrintPreviewWebContentDelegate subclass.
Add a consolidated WebDialogWebContentsDelegateViews instead.
(ensures WebView focus and forwards dialog shortcut keys)

TODO(followup): Additional WebUI dialog creation cleanup.

BUG=410158, 368691
TEST="Show as tab" doesn't crash popups with print dialogs. Focusing print dialog <-> omnibox works.
R=ben@chromium.org

Committed: https://crrev.com/4db9fd60d24d06580dbff65fa648a2515e599e22
Cr-Commit-Position: refs/heads/master@{#293961}

[msw, 2014-09-04 22:52:45]

Patchset #3 (id:40001) has been deleted

[msw, 2014-09-04 22:52:49]

Patchset #2 (id:20001) has been deleted

[msw, 2014-09-04 22:58:36]

msw@chromium.org changed reviewers:
+ ben@chromium.org

[msw, 2014-09-08 20:18:53]

Patchset #7 (id:160001) has been deleted

[msw, 2014-09-08 20:18:59]

Patchset #6 (id:140001) has been deleted

[msw, 2014-09-08 21:34:59]

Hey Ben, please take a look; thanks!

[Ben Goodger (Google), 2014-09-09 16:03:04]

lgtm

[msw, 2014-09-09 16:33:23]

The CQ bit was checked by msw@chromium.org

[commit-bot: I haz the power, 2014-09-09 16:53:45]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/msw@chromium.org/538203002/180001

[commit-bot: I haz the power, 2014-09-09 17:30:31]

Committed patchset #6 (id:180001) as 6eac0438153f5ebab2608ce7cb2a8fa8d8135410

[commit-bot: I haz the power, 2014-09-10 03:54:06]

Patchset 6 (id:??) landed as
https://crrev.com/4db9fd60d24d06580dbff65fa648a2515e599e22
Cr-Commit-Position: refs/heads/master@{#293961}