Reland: Fix and expand upon BubbleDelegateTests.

Reland: Fix and expand upon BubbleDelegateTests.
This is a continuation of https://codereview.chromium.org/10889014
That CL was reverted due to test failures in linux_chromeos and win_aura bots:
http://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20%281%29/builds/10785/steps/views_unittests/logs/stdio
http://build.chromium.org/p/chromium/builders/Win%20Aura/builds/20590/steps/views_unittests/logs/stdio

This revised CL adds a workaround hack for Aura to activate an unrelated Widget before closing the anchor/owner widgets, so that aura::test::TestActivationClient::OnWindowDestroyed doesn't try to activate destroyed windows.

Original CL description:
===============================================
Fix and expand upon BubbleDelegateTests.

BubbleDelegateTest.ResetAnchorWidget was previously failing and crashing because of it's widget ownership pattern and lack of close_on_deactivate.

Add TestWidgetObserver to observe bubbles closing.
Ensure the bubble widget closes as expected in each test.

BUG=none
TEST=unit tests pass

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=154558

[msw, 2012-08-31 02:23:32]

Hey Ben, please take a look; any advice on how to nix the hack is appreciated!

[Ben Goodger (Google), 2012-08-31 22:40:57]

lgtm

[commit-bot: I haz the power, 2012-08-31 22:43:38]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/msw@chromium.org/10920028/3002

[commit-bot: I haz the power, 2012-09-01 01:15:15]

Change committed as 154558