Add mxcai and dominickn to c/b/apps/intent_helper/OWNERS

Bug: None
Change-Id: I8263599f3f217e19c66fb207662a0752d8686b9b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1562298Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Maggie Cai <mxcai@chromium.org>
Commit-Queue: David Jacobo <djacobo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#649735}

chrome/browser/apps/intent_helper/OWNERS

+dominickn@chromium.org
+mxcai@chromium.org
 # For ARC related code
 djacobo@chromium.org
 # For ARC related code, backup reviewers