Add kbr@chromium.org to Source/platform/OWNERS; already core/ OWNER.
Add kbr@chromium.org to Source/platform/OWNERS; already core/ OWNER.

BUG=

Review URL: https://codereview.chromium.org/102213010

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@164253 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs