FrameBuffer::NextFrame now return a ReturnReason and take an additional std::unique_ptr<FrameObject>* as output parameter.

In order to distinguish between a return caused by the FrameBuffer
being stopped and a return caused by a timeout we now return
a ReturnReason.

BUG=webrtc:5514
R=danilchap@webrtc.org, mflodman@webrtc.org

Review URL: https://codereview.webrtc.org/2302473002 .

Cr-Commit-Position: refs/heads/master@{#14065}
diff --git a/webrtc/modules/video_coding/frame_buffer2_unittest.cc b/webrtc/modules/video_coding/frame_buffer2_unittest.cc
index 674ae29..ad776df 100644
--- a/webrtc/modules/video_coding/frame_buffer2_unittest.cc
+++ b/webrtc/modules/video_coding/frame_buffer2_unittest.cc
@@ -135,7 +135,10 @@
   void ExtractFrame(int64_t max_wait_time = 0) {
     crit_.Enter();
     if (max_wait_time == 0) {
-      frames_.emplace_back(buffer_.NextFrame(0));
+      std::unique_ptr<FrameObject> frame;
+      FrameBuffer::ReturnReason res = buffer_.NextFrame(0, &frame);
+      if (res != FrameBuffer::ReturnReason::kStopped)
+        frames_.emplace_back(std::move(frame));
       crit_.Leave();
     } else {
       max_wait_time_ = max_wait_time;
@@ -170,7 +173,11 @@
         if (tfb->tear_down_)
           return false;
 
-        tfb->frames_.emplace_back(tfb->buffer_.NextFrame(tfb->max_wait_time_));
+        std::unique_ptr<FrameObject> frame;
+        FrameBuffer::ReturnReason res =
+            tfb->buffer_.NextFrame(tfb->max_wait_time_, &frame);
+        if (res != FrameBuffer::ReturnReason::kStopped)
+          tfb->frames_.emplace_back(std::move(frame));
       }
     }
   }