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.cc b/webrtc/modules/video_coding/frame_buffer2.cc
index dab7832..766e6a0 100644
--- a/webrtc/modules/video_coding/frame_buffer2.cc
+++ b/webrtc/modules/video_coding/frame_buffer2.cc
@@ -52,7 +52,9 @@
       stopped_(false),
       protection_mode_(kProtectionNack) {}
 
-std::unique_ptr<FrameObject> FrameBuffer::NextFrame(int64_t max_wait_time_ms) {
+FrameBuffer::ReturnReason FrameBuffer::NextFrame(
+    int64_t max_wait_time_ms,
+    std::unique_ptr<FrameObject>* frame_out) {
   int64_t latest_return_time = clock_->TimeInMilliseconds() + max_wait_time_ms;
   int64_t now = clock_->TimeInMilliseconds();
   int64_t wait_ms = max_wait_time_ms;
@@ -63,7 +65,7 @@
       rtc::CritScope lock(&crit_);
       frame_inserted_event_.Reset();
       if (stopped_)
-        return std::unique_ptr<FrameObject>();
+        return kStopped;
 
       now = clock_->TimeInMilliseconds();
       wait_ms = max_wait_time_ms;
@@ -115,9 +117,10 @@
         decoded_frames_.insert(next_frame_it->first);
         std::unique_ptr<FrameObject> frame = std::move(next_frame_it->second);
         frames_.erase(frames_.begin(), ++next_frame_it);
-        return frame;
+        *frame_out = std::move(frame);
+        return kFrameFound;
       } else {
-        return std::unique_ptr<FrameObject>();
+        return kTimeout;
       }
     }
   }
diff --git a/webrtc/modules/video_coding/frame_buffer2.h b/webrtc/modules/video_coding/frame_buffer2.h
index 0af2bf9..d0f8961 100644
--- a/webrtc/modules/video_coding/frame_buffer2.h
+++ b/webrtc/modules/video_coding/frame_buffer2.h
@@ -36,6 +36,8 @@
 
 class FrameBuffer {
  public:
+  enum ReturnReason { kFrameFound, kTimeout, kStopped };
+
   FrameBuffer(Clock* clock,
               VCMJitterEstimator* jitter_estimator,
               VCMTiming* timing);
@@ -44,9 +46,14 @@
   void InsertFrame(std::unique_ptr<FrameObject> frame);
 
   // Get the next frame for decoding. Will return at latest after
-  // |max_wait_time_ms|, with either a managed FrameObject or an empty
-  // unique ptr if there is no available frame for decoding.
-  std::unique_ptr<FrameObject> NextFrame(int64_t max_wait_time_ms);
+  // |max_wait_time_ms|.
+  //  - If a frame is availiable within |max_wait_time_ms| it will return
+  //    kFrameFound and set |frame_out| to the resulting frame.
+  //  - If no frame is available after |max_wait_time_ms| it will return
+  //    kTimeout.
+  //  - If the FrameBuffer is stopped then it will return kStopped.
+  ReturnReason NextFrame(int64_t max_wait_time_ms,
+                         std::unique_ptr<FrameObject>* frame_out);
 
   // Tells the FrameBuffer which protection mode that is in use. Affects
   // the frame timing.
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));
       }
     }
   }