Introduce Promises.

We would like to introduce DOM/Promises[1].
Unlike ordinary DOM objects, the internal state is held as a JavaScript object to avoid leaks.
To achieve this, WebCore::Promise class is empty (it is added to make the IDL processor happy) and all methods are marked as CUSTOM.
Perhaps we will make the IDL processor support this style in a future CL.

As a first step, This CL contains Promise constructor only.
The remaining part will be implemented in another CL.

[1] https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/9q5kP0eMQc8 
BUG=243345
R=abarth@chromium.org
TESTS=fast/js/Promise-init.html

Review URL: https://chromiumcodereview.appspot.com/17505004

git-svn-id: svn://svn.chromium.org/blink/trunk@152943 bbb929c8-8fbe-4397-9dbb-9b2b20218538
13 files changed