Refactored the call box tree

BUG=chromium:272493
TEST=run_all_tests.py

Change-Id: I688aaa705bc923f9af97161401b787526de05d46
Reviewed-on: https://chromium-review.googlesource.com/182870
Reviewed-by: Ben Chan <[email protected]>
Tested-by: Byron Kubert <[email protected]>
Commit-Queue: Byron Kubert <[email protected]>
8 files changed