Teach the preload scanner about the 'nonce' attribute.

The 'nonce' attribute helps determine whether a particular script or
stylesheet can be loaded in the context of a page's Content Security
Policy. Currently, the preload scanner ignores this attribute, which
means we might end up not preloading something we ought to preload.

This patch teaches the preload scanner to store this data and pass it
on with the preload request.

R=yoav@yoav.ws

Review-Url: https://codereview.chromium.org/2148723002
Cr-Commit-Position: refs/heads/master@{#405446}
4 files changed