[desktopCapture Sample] deprecate URL.createObjectURL

URL.createObjectURL with media streams is deprecated and will be removed
in M68, around July 2018. Please use HTMLMediaElement.srcObject instead.

Bug: 826088
Change-Id: Ic1793ce689b0dad667ba80065b13bfafb1b84c79
Reviewed-on: https://chromium-review.googlesource.com/981601Reviewed-by: Ken Rockot <rockot@chromium.org>
Commit-Queue: Weiyong Yao <braveyao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#546152}

chrome/common/extensions/docs/examples/api/desktopCapture/app.js

@@ -65,7 +65,11 @@ function getUserMediaError(error) {
 function gotStream(stream) {
   console.log('Received local stream', stream);
   var video = document.querySelector('video');
+  try {
+    video.srcObject = stream;
+  } catch (error) {
     video.src = URL.createObjectURL(stream);
+  }
   stream.onended = function() { console.log('Ended'); };
 
   pc1 = new RTCPeerConnection();
@@ -107,7 +111,11 @@ function onCreateOfferSuccess(desc) {
 function gotRemoteStream(event) {
   // Call the polyfill wrapper to attach the media stream to this element.
   console.log('hitting this code');
+  try {
+    remoteVideo.srcObject = event.stream;
+  } catch (error) {
     remoteVideo.src = URL.createObjectURL(event.stream);
+  }
 }
 
 function onCreateAnswerSuccess(desc) {