Clean up WebCustomElement and other FIXMEs post Chromium r218769

BUG=273126
TEST=fast/dom/custom, browser_tests --gtest_filter=WebViewTest.*

Review URL: https://chromiumcodereview.appspot.com/23129029

git-svn-id: svn://svn.chromium.org/blink/trunk@156734 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add a webexposed test for Custom Elements.

The expected result in virtual/stable/webexposed ensures that Custom
Elements don't affect the processing of elements by default.

BUG=234509

Review URL: https://chromiumcodereview.appspot.com/23417002

git-svn-id: svn://svn.chromium.org/blink/trunk@156735 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Change devicePixelRatio to include full-page zoom

Change window.devicePixelRatio to take full-page zoom (but not pinch
zoom) into account. Matches behavior of FF and IE11.

Approved to ship as part of blink launch process:
https://groups.google.com/a/chromium.org/d/topic/blink-dev/RyUSi3zdumQ/discussion

BUG=279430

Review URL: https://chromiumcodereview.appspot.com/23441002

git-svn-id: svn://svn.chromium.org/blink/trunk@156736 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Implement Custom Elements class-side inheritance.

DOM elements and ES6 do something called "class-side inheritance"
where not only does an instance of subtype B's prototype point to base
type A's prototype, the B constructor's prototype is A's
constructor. This means that B.FOO works where FOO is a static
operation or const attribute (in the WebIDL sense) of A.

This is described in this proposal:
<https://www.w3.org/Bugs/Public/show_bug.cgi?id=22920>

BUG=271466

Review URL: https://chromiumcodereview.appspot.com/23386003

git-svn-id: svn://svn.chromium.org/blink/trunk@156737 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Revert 156733 "Refactoring DrawLooper so that it can apply shado..."

> Refactoring DrawLooper so that it can apply shadow effects as skia image filters
> 
> This fixes a bug where a bitmap's alpha channel was not being blurred when
> rendering 2D canvas shadows.
> 
> BUG=100703
> R=senorblanco
> TEST=LayoutTest fast/canvas/canvas-drawImage-shadow-blur.html
> 
> Review URL: https://chromiumcodereview.appspot.com/23102018

TBR=junov@chromium.org

Review URL: https://codereview.chromium.org/23507002

git-svn-id: svn://svn.chromium.org/blink/trunk@156738 bbb929c8-8fbe-4397-9dbb-9b2b20218538