Revert of Remove deprecated extension notification from WebstoreStartupInstallerTest

Revert of Remove deprecated extension notification from WebstoreStartupInstallerTest (https://codereview.chromium.org/437603002/)

Reason for revert:
Broke several tests on Linux Asan/Lsan:

http://build.chromium.org/p/chromium.memory/builders/Linux%20ASan%20LSan%20Tests%20%282%29/builds/5662/steps/browser_tests/logs/LimitedAccept

http://build.chromium.org/p/chromium.memory/builders/Linux%20ASan%20LSan%20Tests%20%283%29/builds/5973/steps/browser_tests/logs/Cancel

http://build.chromium.org/p/chromium.memory/builders/Linux%20ASan%20LSan%20Tests%20%283%29/builds/5973/steps/browser_tests/logs/Accept

E.g.

==21932==ERROR: AddressSanitizer: heap-use-after-free on address 0x611000210570 at pc 0x00000c56a19d bp 0x7fff04951d00 sp 0x7fff04951cf8
READ of size 8 at 0x611000210570 thread T0 (browser_tests)
    #0 0xc56a19c in begin third_party/libc++/trunk/include/vector:1417:12
    #1 0xc56a19c in RemoveObserver base/observer_list.h:168
    #2 0xc56a19c in extensions::ExtensionRegistry::RemoveObserver(extensions::ExtensionRegistryObserver*) extensions/browser/extension_registry.cc:37
    #3 0x13a2de2 in RemoveAll base/scoped_observer.h:39:7
    #4 0x13a2de2 in ~ScopedObserver base/scoped_observer.h:22
    #5 0x13a2de2 in CommandLineWebstoreInstall::~CommandLineWebstoreInstall() chrome/browser/extensions/webstore_startup_installer_browsertest.cc:250

Original issue's description:
> Remove deprecated extension notification from WebstoreStartupInstallerTest
> 
> BUG=354046
> TEST=browser_tests WebstoreStartupInstallerTest.*
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=287154

TBR=kalman@chromium.org,limasdf@gmail.com
NOTREECHECKS=true
NOTRY=true
BUG=354046
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=287169

[pneubeck (no reviews), 2014-08-02 07:06:30]

Created Revert of Remove deprecated extension notification from
WebstoreStartupInstallerTest

[commit-bot: I haz the power, 2014-08-02 07:07:37]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/pneubeck@chromium.org/428123004/1

[commit-bot: I haz the power, 2014-08-02 07:09:24]

Change committed as 287169