Load about:blank ahead of the tests at the leak detection

This patch fixes the way about:blank is loaded ahead of the tests for
leak detection. By the previous patch r247209, the leak detection is
implemented. The detection is performed by comparing the number of DOM
objects at about:blank which is loaded between the tests. So, ahead of
any tests, about:blank should be loaded. By the previous patch, this was
implemented as a dummy tests, but was not good in many senses. For
example, the webkit_test_runner.py would have to ignore this dummy test
but this would be hacky. This patch fixes these problems by loading
about:blank in a direct method.

Without the leak detection, the flow of the tests is below:
1. For each tests:
..1. Prepare the test at WebKitTestController::PrepareForLayoutTest
..2. Load the test URL
..3. Start the test by WebKitTestController::SendTestConfiguration
..4. Execute the test at the renderer process
..5. Quit the test at WebKitTestController::OnResetDone

With the leak detection, the flow of the tests will be below:
1. For each following test:
..1. Prepare the test at WebKitTestController::PrepareForLayoutTest
..2. Load the test URL
..3. Start the test by WebKitTestController::SendTestConfiguration
..4. Execute the test at the renderer process
..5. Start trying the leak detection at WebKitTestController::OnResetDone
..6. Quit the test at WebKitTestController::OnLeakDetectionDone

See also:
https://docs.google.com/a/chromium.org/document/d/1sFAsZxeISKnbGdXoLZlB2tDZ8pvO102ePFQx6TX4X14/edit#

BUG=332630

Review URL: https://codereview.chromium.org/148213003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251655 0039d316-1c4b-4281-b951-d872f2087c98
No PasswordStoreFactory in PasswordManager and PasswordFormManager unittests

BUG=342683

Review URL: https://codereview.chromium.org/164493006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251656 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251656
Fixing crash when DRIVER_INFO_6::pszMfgName is NULL

BUG=344291
TBR=noamsml

Review URL: https://codereview.chromium.org/169373002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251657 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251657