Move videosourceinterface to api.

VideoSourceInterface is clearly an integral part of
mediastreaminterface.h already, so moving that interface to api makes
sense. This also resolves a circular dependency in call/.

Bug: webrc:6828
Change-Id: Ic1862f118363b0b55a235a9c0c35d9adc647184c
Reviewed-on: https://webrtc-review.googlesource.com/37500
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Commit-Queue: Patrik Höglund <phoglund@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21498}
diff --git a/api/mediastreaminterface.h b/api/mediastreaminterface.h
index 1350b29..3273c6d 100644
--- a/api/mediastreaminterface.h
+++ b/api/mediastreaminterface.h
@@ -28,7 +28,7 @@
 // relying on them; they were previously transitively included by
 // mediachannel.h, which is no longer a dependency of this file.
 #include "api/videosinkinterface.h"
-#include "media/base/videosourceinterface.h"
+#include "api/videosourceinterface.h"
 #include "modules/audio_processing/include/audio_processing_statistics.h"
 #include "rtc_base/ratetracker.h"
 #include "rtc_base/refcount.h"