This CL makes the following replacements:

1.
base::MessageLoopForUIorIO::current()->Run()/RunUntilIdle();
becomes
// This ASSERT_TRUE replaces the DCHECK in
// MessageLoopForUIorIO::current().
ASSERT_TRUE(base::MessageLoopForUIorIO::IsCurrent());
base::RunLoop().Run()/RunUntilIdle();

2.
message_loop_for_ui_or_io.Run()/RunUntilIdle();
becomes
// The ASSERT_TRUE is present only if it isn't obvious that
// the current thread runs a MessageLoopForUIorIO (e.g.
// because it isn't instantiated in the current file).
ASSERT_TRUE(base::MessageLoopForUIorIO::IsCurrent());
base::RunLoop().Run()/RunUntilIdle();

BUG=616447

Review-Url: https://codereview.chromium.org/2354333002
Cr-Commit-Position: refs/heads/master@{#420342}