Clean up ExtensionServiceTest.

- Make InstallCrx, PackAndInstallCrx return the installed Extension*.
- Change StartCrxInstall callers to use InstallCrx.
- Fix dubious use of ScopedTempDir in PackAndInstallCrx.
- Add an InstallState enum for the above functions.
- Remove all uses of extensions()->at(), since ExtensionSet won't support it.

BUG=104091
TEST=unit_tests


Review URL: http://codereview.chromium.org/8598028

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@111213 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/extensions/extension_service_unittest.h

@@ -57,7 +57,7 @@ class ExtensionServiceTestBase : public testing::Test {
   FilePath data_dir_;
   // Owned by |profile_|.
   ExtensionService* service_;
-  size_t total_successes_;
+  size_t expected_extensions_count_;
   content::TestBrowserThread ui_thread_;
   content::TestBrowserThread db_thread_;
   content::TestBrowserThread webkit_thread_;