Move all codec specific definitions from modules_include

This CL moves all codec specific definitions into their own
header files in the respective codec directory, and replaces
it with an include in the top level directory.

This is to facilitate getting the code out of the header files.

No behavioral changes are expected.

BUG=webrtc:6842

Review-Url: https://codereview.webrtc.org/2555993003
Cr-Commit-Position: refs/heads/master@{#15623}

webrtc/modules/video_coding/codecs/interface/common_constants.h

@@ -0,0 +1,26 @@
+/*
+ *  Copyright (c) 2016 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.
+ */
+
+// This file contains constants that are used by multiple global
+// codec definitions (modules/video_coding/codecs/*/include/*_globals.h)
+
+#ifndef WEBRTC_MODULES_VIDEO_CODING_CODECS_INTERFACE_COMMON_CONSTANTS_H_
+#define WEBRTC_MODULES_VIDEO_CODING_CODECS_INTERFACE_COMMON_CONSTANTS_H_
+
+namespace webrtc {
+
+const int16_t kNoPictureId = -1;
+const int16_t kNoTl0PicIdx = -1;
+const uint8_t kNoTemporalIdx = 0xFF;
+const int kNoKeyIdx = -1;
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_VIDEO_CODING_CODECS_INTERFACE_COMMON_CONSTANTS_H_