Signal exceptions if start/stop is called out-of-order or too many times.

LayoutTests/webaudio/dom-exceptions-expected.txt

Index: LayoutTests/webaudio/dom-exceptions-expected.txt
diff --git a/LayoutTests/webaudio/dom-exceptions-expected.txt b/LayoutTests/webaudio/dom-exceptions-expected.txt
index 604f309aa4a4e7afed15e6cad7b1840b5bb79950..1dbe9aceb34c8a9725a873646b451ca777bc3d2f 100644
--- a/LayoutTests/webaudio/dom-exceptions-expected.txt
+++ b/LayoutTests/webaudio/dom-exceptions-expected.txt
@@ -51,10 +51,27 @@ PASS source.start() did not throw exception.
 PASS source.stop() did not throw exception.
 PASS source = context.createBufferSource() did not throw exception.
 PASS source.start() did not throw exception.
+PASS source = context.createBufferSource() did not throw exception.
+PASS source.buffer = buffer did not throw exception.
+PASS source.stop() threw exception InvalidStateError: Failed to execute 'stop' on 'OscillatorNode': cannot call stop without calling start first..
+PASS source = context.createBufferSource() did not throw exception.
+PASS source.buffer = buffer did not throw exception.
+PASS source.start() did not throw exception.
+PASS source.start() threw exception InvalidStateError: Failed to execute 'start' on 'AudioBufferSourceNode': cannot call start more than once..
+PASS source = context.createBufferSource() did not throw exception.
+PASS source.buffer = buffer did not throw exception.
+PASS source.start() did not throw exception.
 PASS source.stop() did not throw exception.
+PASS source.stop() threw exception InvalidStateError: Failed to execute 'stop' on 'OscillatorNode': cannot call stop more than once..
 PASS source = context.createOscillator() did not throw exception.
 PASS source.start() did not throw exception.
 PASS source.stop() did not throw exception.
+PASS osc = context.createOscillator() did not throw exception.
+PASS osc.stop() threw exception InvalidStateError: Failed to execute 'stop' on 'OscillatorNode': cannot call stop without calling start first..
+PASS osc1 = context.createOscillator() did not throw exception.
+PASS osc1.start() did not throw exception.
+PASS osc1.stop() did not throw exception.
+PASS osc1.stop() threw exception InvalidStateError: Failed to execute 'stop' on 'OscillatorNode': cannot call stop more than once..
 PASS successfullyParsed is true
 
 TEST COMPLETE