Merge 152659 - mac/rlz: Remove an incorrect check

Merge 152659 - mac/rlz: Remove an incorrect check

As a comment in the ScopedRlzValueStoreLock destructor explains:

  // Check that "store_ set" => "file_lock acquired". The converse isn't true,
  // for example if the rlz data file can't be read.

So don't CHECK when that happens, instead treat it like lock acquisition failures:
Silently drop events when that happens. I added a unit test for this scenario.

Also pass O_RDWR to open(), as posix requires one of O_READ, O_WRITE, or O_RDWR.

BUG=143950
Review URL: https://chromiumcodereview.appspot.com/10828424

TBR=thakis@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=152888