Add canvas blending modes under a runtime flag

LayoutTests/fast/canvas/script-tests/canvas-blend-image.js

 description("Series of tests to ensure correct results on applying different blend modes.");
 
 var tmpimg = document.createElement('canvas');
 tmpimg.width = 200;
 tmpimg.height = 200;
 ctx = tmpimg.getContext('2d');
 
 // Create the image for blending test with images.
 var img = document.createElement('canvas');
 img.width = 200;
@@ skipping 50 matching lines @@
   ],
   ['color-dodge',
          [[0, 0, 255, 255],[0, 0, 255, 255],[0, 0, 255, 255],[0, 0, 255, 255]],
          [[0, 0, 255, 255],[0, 0, 255, 255],[0, 0, 255, 255],[0, 0, 255, 255]],
          [[128, 0, 127, 255],[128, 128, 127, 255],[0, 64, 127, 255],[0, 0, 255, 255]],
          [[85, 0, 170, 191],[85, 85, 170, 191],[0, 43, 170, 191],[0, 0, 255, 191]]
   ],
   ['color-burn',
          [[0, 0, 255, 255],[0, 0, 255, 255],[0, 0, 255, 255],[0, 0, 255, 255]],
          [[0, 0, 255, 255],[0, 0, 255, 255],[0, 0, 255, 255],[0, 0, 255, 255]],
-         [[128, 0, 127, 255],[128, 128, 127, 255],[0, 0, 127, 255],[0, 0, 255, 255]],
-         [[85, 0, 170, 191],[85, 85, 170, 191],[0, 0, 170, 191],[0, 0, 255, 191]]
+         [[128, 0, 127, 255],[128, 128, 127, 255],[0, 64, 127, 255],[0, 0, 255, 255]],
+         [[85, 0, 170, 191],[85, 85, 170, 191],[0, 42, 170, 191],[0, 0, 255, 191]]
 
   ],
   ['hard-light',
          [[255, 0, 0, 255],[255, 255, 0, 255],[0, 1, 0, 255],[0, 0, 255, 255]],
          [[128, 0, 127, 255],[128, 128, 127, 255],[0, 0, 127, 255],[0, 0, 255, 255]],
          [[255, 0, 0, 255],[255, 255, 0, 255],[0, 65, 0, 255],[0, 0, 255, 255]],
          [[171, 0, 84, 191],[171, 171, 84, 191],[0, 43, 84, 191],[0, 0, 255, 191]]
   ],
   ['soft-light',
          [[0, 0, 255, 255],[0, 0, 255, 255],[0, 0, 255, 255],[0, 0, 255, 255]],
@@ skipping 84 matching lines @@
           
           checkBlendModeResult(blendModes[i][0], testScenario[j][0], blendModes[i][j+1], sigma);
           ctx.restore();                                  
           }
         debug('');
         }
   }
 
 // Run test and allow variation of results.
 prepareTestScenario(5);