Move video_encoder.h and video_decoder.h to /api and create GN targets for them

webrtc/media/engine/fakewebrtcvideoengine.h

Index: webrtc/media/engine/fakewebrtcvideoengine.h
diff --git a/webrtc/media/engine/fakewebrtcvideoengine.h b/webrtc/media/engine/fakewebrtcvideoengine.h
index 2dce2c503fcf67e284ef0d3d84027a6dc7ffd74a..1fd9983c7e8b00c891cde1e82bd845a5e3ead7d0 100644
--- a/webrtc/media/engine/fakewebrtcvideoengine.h
+++ b/webrtc/media/engine/fakewebrtcvideoengine.h
@@ -14,6 +14,7 @@
 #include <map>
 #include <set>
 #include <vector>
+#include <string>
 
 #include "webrtc/base/basictypes.h"
 #include "webrtc/base/criticalsection.h"
@@ -24,8 +25,8 @@
 #include "webrtc/media/engine/webrtcvideodecoderfactory.h"
 #include "webrtc/media/engine/webrtcvideoencoderfactory.h"
 #include "webrtc/modules/video_coding/include/video_error_codes.h"
-#include "webrtc/video_decoder.h"
-#include "webrtc/video_encoder.h"
+#include "webrtc/api/video_decoder.h"
+#include "webrtc/api/video_encoder.h"
 
 namespace cricket {
 static const int kEventTimeoutMs = 10000;