mac: Prepare for -Wunused-functions.

Mostly involves deleting unused code.

BUG=315884

Review URL: https://codereview.chromium.org/63503002

git-svn-id: svn://svn.chromium.org/blink/trunk@161491 bbb929c8-8fbe-4397-9dbb-9b2b20218538
IDL compiler: [ImplementedAs] for methods

BUG=239771
NOTRY=true

Review URL: https://codereview.chromium.org/63643002

git-svn-id: svn://svn.chromium.org/blink/trunk@161492 bbb929c8-8fbe-4397-9dbb-9b2b20218538