Update webrtc::DesktopCapturer clients to implement OnCaptureResult().

OnCaptureCompleted() method in webrtc::DesktopCapturer::Callback is
being replaced with OnCaptureResult(). The new method uses unique_ptr<>
to pass frame ownership, and also gets a Result code that allows to
distinguish between different types of capture errors.

BUG=webrtc:5950

Review-Url: https://codereview.chromium.org/2050353002
Cr-Commit-Position: refs/heads/master@{#400494}
23 files changed