Add validation conformance tests for associated interfaces. Add encoding, decoding and validation for associated interfaces.

Modified Mojo js tmpls to support associated interfaces (encode, decode, default values, validation).
Added codec.AssociatedInterfacePtrInfo and codec.AssociatedInterfaceRequest.
Modify validator.js  validateMessageHeader() to validate v2 messages.
Add to validator.js validateAssociatedInterface & validateAssociatedInterfaceRequest.
Modify validator.js validateArray(...) to validate array of associated InterfacePtrInfo/InterfaceRequest.

BUG=695635

Review-Url: https://codereview.chromium.org/2796253002
Cr-Commit-Position: refs/heads/master@{#464478}