[ObjC ARC] Converts ios/chrome/common:unit_tests to ARC.
Automatically generated ARCMigrate commit
Notable issues:
Separated block_unittest.mm into its own target as it checks memory management and does not apply to an ARC environment. Bug opened at https://bugs.chromium.org/p/chromium/issues/detail?id=690941 to create a test to check for correct interaction of C++ and blocks in the ARC world.
BUG=624363
TEST=None
Review-Url: https://codereview.chromium.org/2681353002
Cr-Commit-Position: refs/heads/master@{#450391}
3 files changed
