Restart capture session if needed on active.

webrtc/sdk/objc/Framework/Classes/avfoundationvideocapturer.mm

Index: webrtc/sdk/objc/Framework/Classes/avfoundationvideocapturer.mm
diff --git a/webrtc/sdk/objc/Framework/Classes/avfoundationvideocapturer.mm b/webrtc/sdk/objc/Framework/Classes/avfoundationvideocapturer.mm
index 1915538f240c242ec392b3a5a6984016af66aa4c..337b13aa8f8d415d0a66a12bd6886edf46d03bcc 100644
--- a/webrtc/sdk/objc/Framework/Classes/avfoundationvideocapturer.mm
+++ b/webrtc/sdk/objc/Framework/Classes/avfoundationvideocapturer.mm
@@ -114,6 +114,10 @@ static cricket::VideoFormat const kIPhone4SFormat =
                selector:@selector(handleCaptureSessionInterruptionEnded:)
                    name:AVCaptureSessionInterruptionEndedNotification
                  object:_captureSession];
+    [center addObserver:self
+               selector:@selector(handleApplicationDidBecomeActive:)
+                   name:UIApplicationDidBecomeActiveNotification
+                 object:[UIApplication sharedApplication]];
 #endif
     [center addObserver:self
                selector:@selector(handleCaptureSessionRuntimeError:)
@@ -351,6 +355,22 @@ static cricket::VideoFormat const kIPhone4SFormat =
   }];
 }
 
+#if TARGET_OS_IPHONE
+
+#pragma mark - UIApplication notifications
+
+- (void)handleApplicationDidBecomeActive:(NSNotification *)notification {
+  [RTCDispatcher dispatchAsyncOnType:RTCDispatcherTypeCaptureSession
+                               block:^{
+    if (self.hasStarted && !self.captureSession.isRunning) {
+      RTCLog(@"Restarting capture session on active.");
+      [self.captureSession startRunning];
+    }
+  }];
+}
+
+#endif  // TARGET_OS_IPHONE
+
 #pragma mark - Private
 
 - (BOOL)setupCaptureSession {