Update WebAudio layout tests to use unprefixed AudioContext.

LayoutTests/webaudio/resources/audioparam-testing.js

 var sampleRate = 44100;
 
 // Information about the starting/ending times and starting/ending values for each time interval.
 var timeValueInfo;
 
 // The difference between starting values between each time interval.
 var startingValueDelta;
       
 // For any automation function that has an end or target value, the end value is based the starting
 // value of the time interval.  The starting value will be increased or decreased by
@@ skipping 387 matching lines @@
 function createAudioGraphAndTest(numberOfTests, initialValue, setValueFunction, automationFunction, testName, maxError, referenceFunction, jumpThreshold)
 {
     if (window.testRunner) {
         testRunner.dumpAsText();
         testRunner.waitUntilDone();
     }
 
     window.jsTestIsAsync = true;
 
     // Create offline audio context.
-    context = new webkitOfflineAudioContext(2, renderLength(numberOfTests), sampleRate);
+    context = new OfflineAudioContext(2, renderLength(numberOfTests), sampleRate);
     var constantBuffer = createConstantBuffer(context, 1, renderLength(numberOfTests));
 
     // We use an AudioGainNode here simply as a convenient way to test the AudioParam
     // automation, since it's easy to pass a constant value through the node, automate the
     // .gain attribute and observe the resulting values.
 
     gainNode = context.createGain();
 
     var bufferSource = context.createBufferSource();
     bufferSource.buffer = constantBuffer;
@@ skipping 12 matching lines @@
                                  setValueFunction,
                                  automationFunction);
     bufferSource.start(0);
       
     context.oncomplete = checkResultFunction(testName,
                                              maxError,
                                              referenceFunction,
                                              jumpThreshold);
     context.startRendering();
 }