[WebRTC] updated to upstream branch 49 and related.

this patch is based on 38d7a7883...226f2f0bd

dom/media/tests/mochitest/test_peerConnection_captureStream_canvas_2d.html

@@ -46,6 +46,18 @@ runNetworkTest(() => {
       // i.e., this order of `requestFrame(); draw();` should work.
       stream.requestFrame();
       h.drawColor(canvas, h.red);
+      var i = 0;
+      return setInterval(function() {
+        try {
+          info("draw " + i ? "green" : "red");
+          h.drawColor(canvas, i ? h.green : h.red);
+          i = 1 - i;
+          stream.requestFrame();
+        } catch (e) {
+          // ignore; stream might have shut down, and we don't bother clearing
+          // the setInterval.
+        }
+      }, 500);
     },
     function PC_REMOTE_WAIT_FOR_REMOTE_RED() {
       return h.waitForPixelColor(mediaElement, h.red, 128,