Clear the FrameBuffer in case of backward jumps in the picture id.

webrtc/modules/video_coding/frame_buffer2_unittest.cc

 /*
  *  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.
  */
 
@@ skipping 401 matching lines @@
   EXPECT_EQ(pid, InsertFrame(pid, 0, ts, false));
   EXPECT_EQ(pid, InsertFrame(pid, 1, ts, true));
   EXPECT_EQ(pid, InsertFrame(pid + 1, 1, ts, true, pid));
   EXPECT_EQ(pid, InsertFrame(pid + 2, 0, ts, false, pid + 1));
   EXPECT_EQ(pid, InsertFrame(pid + 2, 1, ts, true, pid + 1));
   EXPECT_EQ(pid, InsertFrame(pid + 3, 0, ts, false, pid + 2));
   EXPECT_EQ(pid + 3, InsertFrame(pid + 1, 0, ts, false, pid));
   EXPECT_EQ(pid + 3, InsertFrame(pid + 3, 1, ts, true, pid + 2));
 }
 
+TEST_F(TestFrameBuffer2, PictureIdJumpBack) {
+  uint16_t pid = Rand();
+  uint32_t ts = Rand();
+
+  EXPECT_EQ(pid, InsertFrame(pid, 0, ts, false));
+  EXPECT_EQ(pid + 1, InsertFrame(pid + 1, 0, ts + 1, false, pid));
+  ExtractFrame();
+  CheckFrame(0, pid, 0);
+
+  // Jump back in pid but increase ts.
+  EXPECT_EQ(pid - 1, InsertFrame(pid - 1, 0, ts + 2, false));
+  ExtractFrame();
+  ExtractFrame();
+  CheckFrame(1, pid - 1, 0);
+  CheckNoFrame(2);
+}
+
 }  // namespace video_coding
 }  // namespace webrtc