GC plugin: consider references equal to raw pointers.

Unmanaged raw pointers to managed(GC) classes aren't safe across GCs,
hence fields with raw pointer types to such GCed classes are identified
and reported as errors or warnings.

Extend that checking to also apply to reference pointer types.

R=haraken
BUG=420515

Review URL: https://codereview.chromium.org/1274403002

Cr-Commit-Position: refs/heads/master@{#342320}
5 files changed