Implement an infrastructure of Blink-in-JS (The IDL compiler part)

* A design doc is here: https://docs.google.com/a/google.com/document/d/13cT9Klgvt_ciAR3ONGvzKvw6fz9-f6E0FrqYFqfoc8Y/edit

* A full CL is here:
https://codereview.chromium.org/345893002/

* This CL implements the IDL compile part of the Blink-in-JS.

-- IDLExtendedAttributes.txt: Added a [PrivateScriptInterface] IDL extended attribute, which indicates that a given interface is an interface for Blink-in-JS.

-- v8_private_script_interface.py: A code generator for Blink-in-JS' IDL interface.

-- private_script_interface.{h,cpp}: Template files for Blink-in-JS' IDL interface.

-- TestPrivateScriptInterface.idl: Binding tests for a Blink-in-JS' interface.

-- DOMWrapperWorld.{h,cpp}: Added a new dedicated world for Blink-in-JS execution.

* This CL doesn't change any existing behavior, since Blink-in-JS is not yet used by any real code.

BUG=341031

Review URL: https://codereview.chromium.org/331863013

git-svn-id: svn://svn.chromium.org/blink/trunk@176753 bbb929c8-8fbe-4397-9dbb-9b2b20218538