Refactor + enable GN check on video_coding_utility

To avoid the cyclic dependency

BUG=webrtc:6828
NOTRY=True
TBR=magjed@webrtc.org

Review-Url: https://codereview.webrtc.org/2717113002
Cr-Commit-Position: refs/heads/master@{#17116}

webrtc/modules/video_coding/qp_parser.cc

@@ -0,0 +1,28 @@
+/*
+ *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "webrtc/modules/video_coding/qp_parser.h"
+
+#include "webrtc/common_types.h"
+#include "webrtc/modules/video_coding/utility/vp8_header_parser.h"
+
+namespace webrtc {
+
+bool QpParser::GetQp(const VCMEncodedFrame& frame, int* qp) {
+  switch (frame.CodecSpecific()->codecType) {
+    case kVideoCodecVP8:
+      // QP range: [0, 127].
+      return vp8::GetQp(frame.Buffer(), frame.Length(), qp);
+    default:
+      return false;
+  }
+}
+
+}  // namespace webrtc