Revert 166677 "Promote enableHTMLImports flag from test to exper..."

> Promote enableHTMLImports flag from test to experimental.
> 
> This is blink side change to remove --enable-html-imports flag.
> 
> TEST=none
> BUG=317429
> R=dglazkov@chromium.org,esprehn@chromium.org,hayato@chromium.org
> 
> Review URL: https://codereview.chromium.org/157143004

TBR=morrita@chromium.org,dglazkov@chromium.org

Review URL: https://codereview.chromium.org/138163023

git-svn-id: svn://svn.chromium.org/blink/trunk@166877 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Don't layout absolute-pos element when it's only moved

If an absolute-pos element with specified left or right and auto width
is moved vertically, the original code incorrectly treats the move as
a resize causing unnecessary layout.

Should check if left or right actually changed in the movement check.

BUG=328594
TEST=fast/repaint/absolute-layer-specified-left-or-right-auto-width-moved-vertically.html

Review URL: https://codereview.chromium.org/157093003

git-svn-id: svn://svn.chromium.org/blink/trunk@166878 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Move ruby related renderer creation out of RenderObject::createObject

There shouldn't be any tag name checks in RenderObject::createObject, this
patch moves the last ones out and into separate files. This is part of
the ongoing effort to make core rendering and DOM classes not need to know
about each obscure feature (like ruby).

Review URL: https://codereview.chromium.org/159163002

git-svn-id: svn://svn.chromium.org/blink/trunk@166879 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove the "Embedder Custom Elements" feature, it's on by default.

BUG=274833

Review URL: https://codereview.chromium.org/137133010

git-svn-id: svn://svn.chromium.org/blink/trunk@166880 bbb929c8-8fbe-4397-9dbb-9b2b20218538