Unguard Shadow DOM features.

Runtime ShadowDOM flag was already set to true at r169201. This change shouldn't have any effects.

CSSSelector still uses this flag. I'll clean up CSSSelector in another patch.

BUG=336121

Review URL: https://codereview.chromium.org/206033004

git-svn-id: svn://svn.chromium.org/blink/trunk@169912 bbb929c8-8fbe-4397-9dbb-9b2b20218538
drawFocusRing() function in CRC2D draws invalid focus ring.

The function draws a focus ring around the current default path or the given path if the given element is focused.
Currently, the focus ring is drawn incorrectly because it is larger than the given path region.
To solve this problem, we should add focus ring width to dirty rect.

BUG=352976

Review URL: https://codereview.chromium.org/200283003

git-svn-id: svn://svn.chromium.org/blink/trunk@169913 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Removing "using" delclarations that import names from the STL library.

This is as per the the coding guidelines for blink, which disallows
importing names from the STL library through the "using" declarations.

Review URL: https://codereview.chromium.org/199793011

git-svn-id: svn://svn.chromium.org/blink/trunk@169914 bbb929c8-8fbe-4397-9dbb-9b2b20218538