Unify FrameType and VideoFrameType.

Prevents some heap allocation and frame-type conversion since interfaces
mismatch. Also it's less confusing to have one type for this.

BUG=webrtc:5042
R=magjed@webrtc.org, mflodman@webrtc.org, henrik.lundin@webrtc.org, solenberg@webrtc.org, stefan@webrtc.org

Review URL: https://codereview.webrtc.org/1371043003

Cr-Commit-Position: refs/heads/master@{#10320}

webrtc/modules/video_coding/main/source/test/stream_generator.cc

@@ -46,8 +46,8 @@ void StreamGenerator::GenerateFrame(FrameType type,
     ++sequence_number_;
   }
   for (int i = 0; i < num_empty_packets; ++i) {
-    packets_.push_back(GeneratePacket(
-        sequence_number_, timestamp, 0, false, false, kFrameEmpty));
+    packets_.push_back(GeneratePacket(sequence_number_, timestamp, 0, false,
+                                      false, kEmptyFrame));
     ++sequence_number_;
   }
 }