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

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 875621293829a4497b5a690a4f68d3f1a0765e2b..55b73ca374773a10757f04f16471c6b6eb75e7da 100644
--- a/Source/modules/webaudio/AudioBufferSourceNode.cpp
+++ b/Source/modules/webaudio/AudioBufferSourceNode.cpp
@@ -28,7 +28,9 @@
 
 #include "modules/webaudio/AudioBufferSourceNode.h"
 
+#include "bindings/v8/ExceptionMessages.h"
 #include "bindings/v8/ExceptionState.h"
+#include "core/dom/ExceptionCode.h"
 #include "core/page/PageConsole.h"
 #include "platform/audio/AudioUtilities.h"
 #include "modules/webaudio/AudioContext.h"
@@ -381,19 +383,38 @@ unsigned AudioBufferSourceNode::numberOfChannels()
     return output(0)->numberOfChannels();
 }
 
-void AudioBufferSourceNode::start(double when)
+void AudioBufferSourceNode::start(ExceptionState& es)
 {
-    startPlaying(false, when, 0, buffer() ? buffer()->duration() : 0);
+    startPlaying(false, 0, 0, buffer() ? buffer()->duration() : 0, es);
 }
 
-void AudioBufferSourceNode::start(double when, double grainOffset)
+void AudioBufferSourceNode::start(double when, ExceptionState& es)
 {
-    startPlaying(true, when, grainOffset, buffer() ? buffer()->duration() : 0);
+    startPlaying(false, when, 0, buffer() ? buffer()->duration() : 0, es);
 }
 
-void AudioBufferSourceNode::start(double when, double grainOffset, double grainDuration)
+void AudioBufferSourceNode::start(double when, double grainOffset, ExceptionState& es)
 {
-    startPlaying(true, when, grainOffset, grainDuration);
+    startPlaying(true, when, grainOffset, buffer() ? buffer()->duration() : 0, es);
+}
+
+void AudioBufferSourceNode::start(double when, double grainOffset, double grainDuration, ExceptionState& es)
+{
+    startPlaying(true, when, grainOffset, grainDuration, es);
+}
+
+void AudioBufferSourceNode::startPlaying(bool isGrain, double when, double grainOffset, double grainDuration, ExceptionState& es)
+{
+    if (m_playbackState != UNSCHEDULED_STATE) {
+        es.throwDOMException(
+            InvalidStateError,
+            ExceptionMessages::failedToExecute(
+                "start",
+                nodeTypeName(),
+                "cannot call start more than once."));
+        return;
+    }
+    startPlaying(isGrain, when, grainOffset, grainDuration);
 }
 
 void AudioBufferSourceNode::startPlaying(bool isGrain, double when, double grainOffset, double grainDuration)
@@ -419,12 +440,6 @@ void AudioBufferSourceNode::startPlaying(bool isGrain, double when, double grain
         grainDuration = max(0.0, grainDuration);
         grainDuration = min(maxDuration, grainDuration);
         m_grainDuration = grainDuration;
-
-    } else {
-        // Until crbug.com/306139 is implemented, we initialize m_grainOffset and m_grainDuration
-        // again.
-        m_grainOffset = 0.0;
-        m_grainDuration = DefaultGrainDuration;
     }
 
     m_isGrain = isGrain;