Implement an infrastructure of Blink-in-JS (PrivateScriptController 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 PrivateScriptController part of Blink-in-JS.

-- PrivateScriptController::run() is a method to invoke JavaScript code. PrivateScriptController::run() is called from auto-generated code for PrivateScript interfaces.

-- PrivateScriptController.js caches all JavaScript code of PrivateScripts into window.installedClasses.

-- make_private_script_source.py converts a JavaScript file into byte stream and writes it to gen/blink/bindings/PrivateScriptSources.h

* This CL changes no behavior, since there is no customers of Blink-in-JS yet.

BUG=341031

Review URL: https://codereview.chromium.org/353553003

git-svn-id: svn://svn.chromium.org/blink/trunk@176901 bbb929c8-8fbe-4397-9dbb-9b2b20218538
UI tunings of repaint overlay

Tune some UIs of repaint overlay to improve its usability:

- Disable minimum-repaint related UI elements when not applicable to let
  user know when minimum-repaint is not available;

- Add 'overlay' link whenever repaint rects or minimum repaint exist.

Review URL: https://codereview.chromium.org/346283003

git-svn-id: svn://svn.chromium.org/blink/trunk@176902 bbb929c8-8fbe-4397-9dbb-9b2b20218538