Allow WebRTC tests that watch for black frames to be off by one.

content/test/data/media/webrtc_test_utilities.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // These must match with how the video and canvas tags are declared in html.
 const VIDEO_TAG_WIDTH = 320;
 const VIDEO_TAG_HEIGHT = 240;
 
 // Fake video capture background green is of value 135.
 const COLOR_BACKGROUND_GREEN = 135;
@@ skipping 169 matching lines @@
     if (pixels[i] != previousPixels[i]) {
       return true;
     }
   }
   return false;
 }
 
 function isVideoBlack(pixels) {
   for (var i = 0; i < pixels.length; i++) {
     // |pixels| is in RGBA. Ignore the alpha channel.
-    if (pixels[i] != 0 && (i + 1) % 4 != 0) {
+    // 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) {
       return false;
     }
   }
   return true;
 }
 
 // This function matches |left| and |right| and fails the test if the
 // values don't match using normal javascript equality (i.e. the hard
 // types of the operands aren't checked).
 function assertEquals(expected, actual) {
   if (actual != expected) {
     failTest("expected '" + expected + "', got '" + actual + "'.");
   }
 }
 
 function assertNotEquals(expected, actual) {
   if (actual === expected) {
     failTest("expected '" + expected + "', got '" + actual + "'.");
   }
 }