Add an appearance test for password generation feature.

If the password genration feature is enabled, additional code in WebCore is
executed and we'd like to test it.
We introduce a setting and an InternalSettings function to enable the code to
add PasswordGeneratorButtonElement.

The test result contains some expected errors.

BUG=306882

Review URL: https://codereview.chromium.org/31393002

git-svn-id: svn://svn.chromium.org/blink/trunk@160061 bbb929c8-8fbe-4397-9dbb-9b2b20218538
IDL compiler: [RaisesException], [Getter/SetterRaisesException] for setters

Docs:
https://sites.google.com/a/chromium.org/dev/blink/webidl/blink-idl-extended-attributes#TOC-RaisesException-m-

BUG=239771
NOTRY=true

Review URL: https://codereview.chromium.org/31763002

git-svn-id: svn://svn.chromium.org/blink/trunk@160062 bbb929c8-8fbe-4397-9dbb-9b2b20218538