Credential Manager: stub out `navigator.credentials`.

This patch implements NavigatorCredentials, and stubs out a single method
of CredentialsContainer: 'request()'. Currently that method only returns
and resolves a promise. Eventually, it will do something slightly more
exciting and interesting.

BUG=400674

Review URL: https://codereview.chromium.org/449013002

git-svn-id: svn://svn.chromium.org/blink/trunk@179799 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add WTF_LOG_ALWAYS and use it in PrivateScriptRunner

Currently fprintf is the only way to log errors in both debug and release builds.
This CL adds a WTF_LOG_ALWAYS macro that logs errors in both builds.

BUG=341031

Review URL: https://codereview.chromium.org/457543002

git-svn-id: svn://svn.chromium.org/blink/trunk@179800 bbb929c8-8fbe-4397-9dbb-9b2b20218538
FontFace should return the same Promise object over multiple calls

This makes FontFace#loaded and #load() return the same instance of
promise on every call. By using ScriptPromiseProperty, we can avoid
a circular reference.

TEST=fast/css/fontface-properties.html
BUG=

Review URL: https://codereview.chromium.org/440313002

git-svn-id: svn://svn.chromium.org/blink/trunk@179801 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Blink-in-JS: Support private scripts in partial interfaces (IDL compiler part)

This is a split CL of https://codereview.chromium.org/457483002/. This CL supports private scripts in partial interfaces in the IDL compiler.

If we have:

  // PartialX.idl
  partial interface X {
    [ImplementedInPrivateScript] void foo();
  };

then the binding code to call in the private script should be generated in V8X.cpp.

BUG=341031

Review URL: https://codereview.chromium.org/450173002

git-svn-id: svn://svn.chromium.org/blink/trunk@179802 bbb929c8-8fbe-4397-9dbb-9b2b20218538
bindings: Makes DOMMatrixReadOnly inherit from ScriptWrappableBase.

BUG=235436

Review URL: https://codereview.chromium.org/456623002

git-svn-id: svn://svn.chromium.org/blink/trunk@179803 bbb929c8-8fbe-4397-9dbb-9b2b20218538