Improve encryptedmedia exception messages.

To make this testable, this patch also makes `video-test.js` exception messages
visible in the test results.

BUG=270033

Review URL: https://codereview.chromium.org/133633002

git-svn-id: svn://svn.chromium.org/blink/trunk@164866 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Implement RefCountedGarbageCollected class for the blink gc infrastructure.

RefCountedGarbageCollected is used to incrementally move objects from
being reference counted to being managed by the Blink garbage collection
infrastructure.

R=erik.corry@gmail.com, haraken@chromium.org, wibling@chromium.org
BUG=

Review URL: https://codereview.chromium.org/133593002

git-svn-id: svn://svn.chromium.org/blink/trunk@164867 bbb929c8-8fbe-4397-9dbb-9b2b20218538
IDL compiler: Document interfaces

This is the last inherited interface!
Straightforward, but affects several places in the code.

BUG=239771
R=haraken

Review URL: https://codereview.chromium.org/132223006

git-svn-id: svn://svn.chromium.org/blink/trunk@164868 bbb929c8-8fbe-4397-9dbb-9b2b20218538