CFI: Add a new debug URL, chrome://badcastcrash.

This URL causes the renderer to intentionally perform a bad cast, which
causes a CFI violation. This allows us to manually test how CFI violations
in the renderer are handled.

BUG=464797
R=avi@chromium.org
TEST=build with cfi_vptr=1, manually navigate to chrome://badcastcrash, verify that "Aw, snap" page appears

Review URL: https://codereview.chromium.org/1266893002

Cr-Commit-Position: refs/heads/master@{#341247}
5 files changed