Allow custom error messages for DCHECK_CALLED_ON_VALID_SEQUENCE().
The release build definition of DCHECK_CALLED_ON_VALID_SEQUENCE macro
breaks when it is used with custom error messages w/ostream operators,
as the macro body is empty and therefore yields a malformed statement.
This CL uses EAT_STREAM_PARAMETERS to correctly blackhole the error message.

(An example of such a error message can be found in weak_ptr.cc, line 20.)

Also modified the sequence checker unit tests to use custom error messages.


R=dcheng@chromium.org
CC=wez@chromium.org

Change-Id: Iead92dbbca06ae8d7499dbae125136a4897dea31
Reviewed-on: https://chromium-review.googlesource.com/517455


Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#475969}