Web Animations: Replace hasIterationDuration with a NaN duration value

Minor clean-up to the code; e.g. this makes writing tests a bit simpler.

BUG=335350

Review URL: https://codereview.chromium.org/154333003

git-svn-id: svn://svn.chromium.org/blink/trunk@166567 bbb929c8-8fbe-4397-9dbb-9b2b20218538
IDL compiler: finish [PutForwards]

* [PerWorldBindings, PutForwards]
* [PutForwards] with extended attributes on the target attribute

Remaining: 3 => 2

BUG=239771
R=haraken
NOTRY=true

Review URL: https://codereview.chromium.org/156233003

git-svn-id: svn://svn.chromium.org/blink/trunk@166568 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Use ScopedPersistent for persistent handles in V8PerContextData

Using ScopedPersistent is safer, since ScopedPersistent will be automaticallly
destructed when the scope is exited.

(Another motivation is that I want to replace all raw persistent handles
with ScopedPersistent/UnsafePersistent in order to verify that persistent
handles don't leak among worlds.)

Review URL: https://codereview.chromium.org/149263005

git-svn-id: svn://svn.chromium.org/blink/trunk@166569 bbb929c8-8fbe-4397-9dbb-9b2b20218538