Simplification WTF::VectorTraitsBase class

WTF::VectorTraitsBase class does not actually need specifications, as its template parameter 'isPod' can be used to define the flags values.
Furthermore assigning flags to 'true' or 'false' directly is error prone (pls. see https://codereview.chromium.org/23819004/).

Review URL: https://chromiumcodereview.appspot.com/23533022

git-svn-id: svn://svn.chromium.org/blink/trunk@157162 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Have Range constructor take a Document reference in argument

Have Range constructor take a Document reference in argument instead of
a pointer as the Document is expected to be non-null. Most callers
already have a reference so this avoids having to convert it into a
pointer.

Also update Range's ownerDocument() to return a reference as it can
never return NULL.

BUG=281400

Review URL: https://chromiumcodereview.appspot.com/23467007

git-svn-id: svn://svn.chromium.org/blink/trunk@157165 bbb929c8-8fbe-4397-9dbb-9b2b20218538
CSS Animations: add interpolation test for border-radius

Border-radius should not be negative: interpolator fails for that case, and 
crashes in the virtual/web-animations-css/animations suite.

BUG=258896

Review URL: https://chromiumcodereview.appspot.com/23537013

git-svn-id: svn://svn.chromium.org/blink/trunk@157169 bbb929c8-8fbe-4397-9dbb-9b2b20218538