Add Chromium-style header guards to the Blink style checker.

Blink header guards should be made of fully qualified paths now that header
includes can be made of full paths. This will also make more sense in the
context of the move of Blink into the Chromium repo. This commit adds
Chromium-style header guards to the whitelist in the Blink style checker. Once
the repo transition is made, this should probably be made the exclusive style.

BUG=360121

Review URL: https://codereview.chromium.org/227233012

git-svn-id: svn://svn.chromium.org/blink/trunk@171007 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Refactoring: Removing variable m_shouldSubmit from HTMLFormElement.cpp

Variable "m_shouldSubmit" is only set to true if the condition dispatchEvent(Event::createCancelableBubble(EventTypeNames::submit)) 
returns true in api prepareForSubmission. And on becoming true it just submit the form. 
Rest everywhere m_shouldSubmit is false. So this patch removes the variable m_shouldSubmit completely and 
change the return type of HTMLFormElement::prepareForSubmission from bool to void.

Review URL: https://codereview.chromium.org/224963005

git-svn-id: svn://svn.chromium.org/blink/trunk@171008 bbb929c8-8fbe-4397-9dbb-9b2b20218538