This is (another) preparation CL for the linked bug. Device monitors are
in capture/ for unknown reasons but they don't belong there, since they
effectively monitor all audio and video devices in the system. Folders
are cheap, so I moved them out, further clearing the way for moving
//media/capture around, and paves the way to reusing functionality that
is now in //device.

BUG=626125

NOPRESUBMIT=true (this CL has the necessary LGTMs but
it hits an incorrect git cl format media presubmit check).

Review-Url: https://codereview.chromium.org/2224643002
Cr-Commit-Position: refs/heads/master@{#411181}