Have DOMPatchSupport and DocumentFragment deal with Document references

Have DOMPatchSupport and DocumentFragment deal with Document references instead
of using pointers with assertions to make sure the pointers are non-null.

The DocumentFragment constructor still takes a Document pointer in argument
because of ShadowRoot which passes 0 as Document until it is set later on
by TreeScope. I need to investigate more to determine if the DocumentFragment
constructor can take a reference in.

BUG=281400

Review URL: https://chromiumcodereview.appspot.com/23453033

git-svn-id: svn://svn.chromium.org/blink/trunk@157237 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Expose latin1 methods in WebString

Needed to plumb header values correctly between Chromium and Blink.

Also temporarily mark a test as flaky in advance of breaking it for a
WebURLLoaderImpl change. When that change lands, the test will be fixed and
switched back.

BUG=276769

Review URL: https://chromiumcodereview.appspot.com/23456013

git-svn-id: svn://svn.chromium.org/blink/trunk@157238 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Revert r154797: "Move isValid/isCurrentColor from Color to StyleColor"

r154797 caused a number of regressions and instead of trying to fix
them one at a time the change is reverted for now.

BUG=272678, 284357
R=leviw@chromium.org

Review URL: https://chromiumcodereview.appspot.com/23581008

git-svn-id: svn://svn.chromium.org/blink/trunk@157239 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Fix bug in check-webkit-style resulting from our PYTHONPATH shenanigans.

pylint was getting confused by our use of unittest2 renamed as unittest; we
need to have Tools/Scripts and Tools/Scripts/webkitpy/thirdparty in sys.path
for this to work correctly, so we also need to export it into PYTHONPATH.
Without this we would occassional get false errors about missing members
in the TestCase classes.

R=ojan@chromium.org
BUG=

Review URL: https://codereview.chromium.org/23756004

git-svn-id: svn://svn.chromium.org/blink/trunk@157240 bbb929c8-8fbe-4397-9dbb-9b2b20218538