Handle the "key" field as opposed to keyIdentifier field.

keyIdentifier will be deprecated soon so we need to move over to the
standardized identifier.

Approved Intent to Remove: https://groups.google.com/a/chromium.org/d/msg/blink-dev/fqnFyoDCOaA/s4WIxZPqAAAJ

BUG=607349
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2045603002
Cr-Commit-Position: refs/heads/master@{#399369}
49 files changed