Bug 1355048: P4. Remove unnecessary test, and make better use of monitor. r=jesup

MozReview-Commit-ID: F5qu7e6opZX

--HG--
extra : rebase_source : b2caf192904b5ead2a6711615938ce298fa564c0

media/webrtc/signaling/src/mediapipeline/MediaPipeline.cpp

@@ -2217,11 +2217,10 @@ public:
                         uint32_t time_stamp,
                         int64_t render_time)
   {
-    ReentrantMonitorAutoEnter enter(monitor_);
-
-    if (buffer_y) {
+    MOZ_ASSERT(buffer_y);
     // Create a video frame using |buffer|.
-      RefPtr<PlanarYCbCrImage> yuvImage = image_container_->CreatePlanarYCbCrImage();
+    RefPtr<PlanarYCbCrImage> yuvImage =
+      image_container_->CreatePlanarYCbCrImage();
 
     PlanarYCbCrData yuvData;
     yuvData.mYChannel = const_cast<uint8_t*>(buffer_y);
@@ -2242,9 +2241,9 @@ public:
       return;
     }
 
+    ReentrantMonitorAutoEnter enter(monitor_);
     image_ = yuvImage;
   }
-  }
 
 private:
   int width_;