Use WebClipboard::Buffer instead of a boolean for Pasteboard state.

This lets a bunch of identical ternary operators be condensed.

BUG=276565

Review URL: https://chromiumcodereview.appspot.com/22812025

git-svn-id: svn://svn.chromium.org/blink/trunk@157715 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Fix crash when when submitting a form with target then detaching that frame.

Regressed in http://src.chromium.org/viewvc/blink/?revision=157613&view=revision

BUG=290396
TEST=fast/forms/form-iframe-target-before-load-detaches.html

Review URL: https://chromiumcodereview.appspot.com/23442025

git-svn-id: svn://svn.chromium.org/blink/trunk@157716 bbb929c8-8fbe-4397-9dbb-9b2b20218538