[DoNotCheckSecurity=Getter] => [DoNotCheckSecurity]

[DoNotCheckSecurity=Getter] is used only one place (Window.opener), and can be eliminated, as the Setter is custom, and checks security there (V8WindowCustom.cpp).

Note that this makes the access control list misleading.

[DoNotCheckSecurity=Setter] is only used one place (Location.href), but this is a real exception, so we have to keep it.
Adding a comment to explain why (changes page, so ok to set).

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

Review URL: https://codereview.chromium.org/77723003

git-svn-id: svn://svn.chromium.org/blink/trunk@162355 bbb929c8-8fbe-4397-9dbb-9b2b20218538