Presentation attributes using -internal-* are ignored!

This change fixes a regression where -internal-* properties
set through presentation attributes would be ignored. The
issue was that the attribute's stylesheet would get the
wrong parsing mode, thus getting rejected at parse time.
The fix introduces a new mode (CSSAttributeMode) that
allows -internal-* but is considered quirks mode.

The regression uncovered an issue with the current logic
where we would wrongly ASSERT when querying an internal
property from the web-inspector.

Finally, we had to fix
Element::addPropertyToPresentationAttributeStyle
that would make presentation attribute's style sheet
inherit the element's parsing mode.

BUG=304114

Review URL: https://codereview.chromium.org/26466004

git-svn-id: svn://svn.chromium.org/blink/trunk@159385 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Fix two small bugs in StringBuilder::substring

I ran into these as part of re-writing Text node attaching:
https://codereview.chromium.org/26129005/

BUG=301981
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/26883003

git-svn-id: svn://svn.chromium.org/blink/trunk@159386 bbb929c8-8fbe-4397-9dbb-9b2b20218538