Remove calls to MessageLoop::current() in content.

Why?
The fact that there's a MessageLoop on the thread is an
unnecessary implementation detail. When browser threads
are migrated to base/task_scheduler, tasks will no longer
have access to a MessageLoop.

These changes were generated manually.

This CL is identical to https://codereview.chromium.org/2105173004/
except for a fix to content/renderer/devtools/devtools_agent.cc

BUG=616447

Review-Url: https://codereview.chromium.org/2123653003
Cr-Commit-Position: refs/heads/master@{#404207}
20 files changed