Bug 932621 - Make sure the latency does not grow up in ScriptProcessorNode. r=ehsan

content/media/webaudio/ScriptProcessorNode.cpp

@@ -111,15 +111,24 @@ public:
       // interval will be very short. |latency - bufferDuration| will be
       // negative, effectively moving back mLatency to a smaller and smaller
       // value, until it crosses zero, at which point we stop dropping buffers
-      // and resume normal operation.
+      // and resume normal operation. This does not work if at the same time,
+      // the MSG thread was also slowed down, so if the latency on the MSG
+      // thread is normal, and we are still dropping buffers, and mLatency is
+      // still more than twice the duration of a buffer, we reset it and stop
+      // dropping buffers.
       float latency = (now - mLastEventTime).ToSeconds();
       float bufferDuration = aBufferSize / mSampleRate;
       mLatency += latency - bufferDuration;
       mLastEventTime = now;
-      if (mLatency > MAX_LATENCY_S || (mDroppingBuffers && mLatency > 0.0)) {
+      if (mLatency > MAX_LATENCY_S ||
+          (mDroppingBuffers && mLatency > 0.0 &&
+           abs(latency - bufferDuration) < bufferDuration)) {
         mDroppingBuffers = true;
         return;
       } else {
+        if (mDroppingBuffers) {
+          mLatency = 0;
+        }
         mDroppingBuffers = false;
       }
     }