Throw DOM exception in insertAdjacentHTML if context becomes null

Align first part of the insertAdjacentHTML implementation with
http://domparsing.spec.whatwg.org/#insertadjacenthtml().

"Let context be the context object's parent.

 If context is null or a document, throw a DOMException with name
 NoModificationAllowedError and terminate these steps."

While the 'or a document' part was previously implemented, the
'context is null' part was not.

BUG=326965

Review URL: https://codereview.chromium.org/110383002

git-svn-id: svn://svn.chromium.org/blink/trunk@163452 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add http/tests/inspector/network/long-script-content.html to SlowTests

TBR=mkwst@chromium.org
BUG=327078

Review URL: https://codereview.chromium.org/93793006

git-svn-id: svn://svn.chromium.org/blink/trunk@163453 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Rework margin-collapsing for self-collapsing blocks
Refactor the way self-collapsing blocks with clearance are positioned so that they
get the correct logical-top position during margin-collapsing.

See also webkit.org/b/119979
BUG=309294

Review URL: https://codereview.chromium.org/75133007

git-svn-id: svn://svn.chromium.org/blink/trunk@163454 bbb929c8-8fbe-4397-9dbb-9b2b20218538