Re-enable local video test with better logging and higher tolerance.

content/test/data/media/webrtc_test_utilities.js

Index: content/test/data/media/webrtc_test_utilities.js
diff --git a/content/test/data/media/webrtc_test_utilities.js b/content/test/data/media/webrtc_test_utilities.js
index 5fd38113882b7c6bf7f9db219850291da9e4d2c6..88fe4b2926dd33cd3c8ea58de24c0f3d3f4e4810 100644
--- a/content/test/data/media/webrtc_test_utilities.js
+++ b/content/test/data/media/webrtc_test_utilities.js
@@ -66,9 +66,14 @@ function detectVideo(videoElementName, predicate, callback) {
   var width = VIDEO_TAG_WIDTH;
   var height = VIDEO_TAG_HEIGHT;
   var videoElement = $(videoElementName);
-  var canvas = $(videoElementName + '-canvas');
   var oldPixels = [];
+  var startTimeMs = new Date().getTime();
   var waitVideo = setInterval(function() {
+    var canvas = $(videoElementName + '-canvas');
+    if (canvas == null) {
+      console.log('Waiting for ' + videoElementName + '-canvas' + ' to appear');
+      return;
+    }
     var context = canvas.getContext('2d');
     context.drawImage(videoElement, 0, 0, width, height);
     var pixels = context.getImageData(0, 0 , width, height / 3).data;
@@ -82,6 +87,12 @@ function detectVideo(videoElementName, predicate, callback) {
       callback(videoElement.videoWidth, videoElement.videoHeight);
     }
     oldPixels = pixels;
+
+    var elapsedTime = new Date().getTime() - startTimeMs;
+    if (elapsedTime > 3000) {
+      startTimeMs = new Date().getTime();
+      console.log('Still waiting for video to satisfy ' + predicate.toString());
+    }
   }, 200);
 }
 
@@ -186,12 +197,18 @@ function isVideoPlaying(pixels, previousPixels) {
   return false;
 }
 
+// Pixels is an array where pixels[0] is the R value for the first pixel,
+// pixels[1] is the G value, and so on.
 function isVideoBlack(pixels) {
   for (var i = 0; i < pixels.length; i++) {
-    // |pixels| is in RGBA. Ignore the alpha channel.
-    // We allow it to be off by 1, to account for rounding errors in YUV
-    // conversion.
-    if (pixels[i] != 0 && pixels[i] != 1 && (i + 1) % 4 != 0) {
+    if ((i + 1) % 4 == 0) {
+      // Ignore the alpha channel.
+      continue;
+    }
+
+    // Should be == 0, but account for rounding errors in YUV conversion.

[kjellander_chromium, 2015/05/12 13:35:46]

Clarify in the comment that a black pixel is == 0. Now it sounds like that is
referring to the condition, which obviously should be > 0 if there were no
rounding errors.

[phoglund_chromium, 2015/05/13 08:47:35]

Done.

+    if (pixels[i] > 3) {
+      console.log('Found nonblack pixel at ' + i + ', was ' + pixels[i]);
       return false;
     }
   }