start/stop method for AudioBufferSourceNodes and OscillatorNodes can take no args.

Source/modules/webaudio/AudioBufferSourceNode.cpp

Index: Source/modules/webaudio/AudioBufferSourceNode.cpp
diff --git a/Source/modules/webaudio/AudioBufferSourceNode.cpp b/Source/modules/webaudio/AudioBufferSourceNode.cpp
index 19aa3e6816aa3fe60e7acc8903a4862976a52c31..dccc704c0684d0d936d371de36a115401df741f6 100644
--- a/Source/modules/webaudio/AudioBufferSourceNode.cpp
+++ b/Source/modules/webaudio/AudioBufferSourceNode.cpp
@@ -372,13 +372,12 @@ unsigned AudioBufferSourceNode::numberOfChannels()
     return output(0)->numberOfChannels();
 }
 
-void AudioBufferSourceNode::startGrain(double when, double grainOffset)
+void AudioBufferSourceNode::start(double when)
 {
-    // Duration of 0 has special value, meaning calculate based on the entire buffer's duration.
-    startGrain(when, grainOffset, 0);
+    AudioScheduledSourceNode::start(when);

[Ken Russell (switch to Gerrit), 2013/10/14 22:54:05]

Are you sure it's correct to delegate to AudioScheduledSourceNode::start here?
The previous implementation used to delegate
AudioBufferSourceNode::startGrain(double, double, double) (which is now
::start(...)), and it looks like it does a *lot* more work for
AudioBufferSourceNodes than AudioScheduledSourceNode::start does.

I assume that there are already existing WebAudio layout tests that cover this
functionality and which work after this change?

[Raymond Toy (Google), 2013/10/28 17:34:57]

The diff is confusing.  A plain start(when) is the simple start method that
doesn't deal with the issues with startGrain.  We didn't really replace
startGrain with start.  startGrain with 2 args is converted to startGrain (now
called start) with 3 args by using a default value for the third arg.
 
Yes, there are tests for start with 2+ args in audiobuffersource-start.html. 
All webaudio layout tests pass.

[Ken Russell (switch to Gerrit), 2013/10/28 20:13:42]

I understand this, but the new code's behavior is significantly different when
calling the simplified start() compared to the version taking more arguments.
The simple start() method delegates up to the superclass, and I think that is a
bad idea, because it will cause the AudioBufferSourceNode to potentially get
into states that are unexpected, especially as the code base evolves.

Because AudioBufferSourceNode shadows some of the invocations of
AudioScheduledSourceNode::start it should shadow all of them. There should be
one start() declaration in the header, taking all three arguments as optional,
just like in the spec.

 }
 
-void AudioBufferSourceNode::startGrain(double when, double grainOffset, double grainDuration)
+void AudioBufferSourceNode::start(double when, double grainOffset, double grainDuration)
 {
     ASSERT(isMainThread());
 
@@ -418,7 +417,7 @@ void AudioBufferSourceNode::startGrain(double when, double grainOffset, double g
 
 void AudioBufferSourceNode::noteGrainOn(double when, double grainOffset, double grainDuration)
 {
-    startGrain(when, grainOffset, grainDuration);
+    start(when, grainOffset, grainDuration);
 }
 
 double AudioBufferSourceNode::totalPitchRate()