Reland: Refactor code that defers extension background page loading

Reland: Refactor code that defers extension background page loading

src/extensions depends on chrome::NOTIFICATION_PROFILE_CREATED to support
deferred loading of extension background pages when the profile isn't ready
yet. This is a layering violation.

* Remove Chrome concepts like "browser window ready" and "profile created"
from ProcessManager. Introduce ProcessManagerDelegate with a general concept
of deferring background page loading.
* Consolidate all the tricky Chrome-specific background page loading rules into
ChromeProcessManagerDelegate. This keeps all the rules in one place. Annotate
each block of special case code with the bug that inspired it.
* Extend unit test coverage for ProcessManager.

This will make it easier to eliminate chrome::NOTIFICATION_PROFILE_DESTROYED
in ProcessManager in a later CL.

(Original CL https://codereview.chromium.org/381283002 broke valgrind bots
because it was initializing left-over BrowserContextKeyedServices from tests
running earlier in the same process.)

BUG=392658
TEST=unit_tests ProcessManagerTest, browser_tests ProcessManagerBrowserTest, manual

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=284593

[James Cook, 2014-07-19 00:19:47]

yoz, please take another look. The differences between patchset 1 and 2 is the
dependency injection I added to deal with the unit tests failure.

If it looks good, please CQ it.

https://codereview.chromium.org/408523005/diff/1/extensions/browser/process_m...
File extensions/browser/process_manager.cc (right):

https://codereview.chromium.org/408523005/diff/1/extensions/browser/process_m...
extensions/browser/process_manager.cc:366: if (!registry)
It turns out in both tests and production code we always have an
ExtensionRegistry, so we can skip a couple if() blocks here and below.

[Yoyo Zhou, 2014-07-21 22:34:51]

LGTM

https://chromiumcodereview.appspot.com/408523005/diff/20001/extensions/browse...
File extensions/browser/lazy_background_task_queue_unittest.cc (right):

https://chromiumcodereview.appspot.com/408523005/diff/20001/extensions/browse...
extensions/browser/lazy_background_task_queue_unittest.cc:28:
ExtensionRegistry::Get(profile)),
I was a bit taken aback here, but I see this test uses TestingProfile.

[James Cook, 2014-07-21 22:54:52]

The CQ bit was checked by jamescook@chromium.org

[commit-bot: I haz the power, 2014-07-21 22:56:45]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/jamescook@chromium.org/408523005/40001

[commit-bot: I haz the power, 2014-07-22 02:13:58]

Change committed as 284593