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

Source/modules/webaudio/AudioScheduledSourceNode.cpp

Index: Source/modules/webaudio/AudioScheduledSourceNode.cpp
diff --git a/Source/modules/webaudio/AudioScheduledSourceNode.cpp b/Source/modules/webaudio/AudioScheduledSourceNode.cpp
index 876da2a1b6c24a6d556685a9ac5a5e17fda89519..7aa6439f9edddb5db49fdfafa14d7f1e4bd2c49a 100644
--- a/Source/modules/webaudio/AudioScheduledSourceNode.cpp
+++ b/Source/modules/webaudio/AudioScheduledSourceNode.cpp
@@ -28,6 +28,9 @@
 
 #include "modules/webaudio/AudioScheduledSourceNode.h"
 
+#include "bindings/v8/ExceptionMessages.h"
+#include "bindings/v8/ExceptionState.h"
+#include "core/dom/ExceptionCode.h"
 #include "core/events/Event.h"
 #include "platform/audio/AudioUtilities.h"
 #include "modules/webaudio/AudioContext.h"
@@ -46,6 +49,7 @@ AudioScheduledSourceNode::AudioScheduledSourceNode(AudioContext* context, float
     , m_startTime(0)
     , m_endTime(UnknownTime)
     , m_hasEndedListener(false)
+    , m_stopCalled(false)
 {
 }
 
@@ -134,34 +138,51 @@ void AudioScheduledSourceNode::updateSchedulingInfo(size_t quantumFrameSize,
     return;
 }
 
-void AudioScheduledSourceNode::start(double when)
+
+void AudioScheduledSourceNode::start(double when, ExceptionState& es)
 {
     ASSERT(isMainThread());
-    if (m_playbackState != UNSCHEDULED_STATE)
+
+    if (m_playbackState != UNSCHEDULED_STATE) {
+        es.throwDOMException(
+            InvalidStateError,
+            ExceptionMessages::failedToExecute(
+                "start",
+                "OscillatorNode",
+                "cannot call start more than once."));
         return;
+    }
 
     m_startTime = when;
     m_playbackState = SCHEDULED_STATE;
 }
 
-void AudioScheduledSourceNode::stop(double when)
+void AudioScheduledSourceNode::stop(double when, ExceptionState& es)
 {
     ASSERT(isMainThread());
-    if (!(m_playbackState == SCHEDULED_STATE || m_playbackState == PLAYING_STATE))
-        return;
-
-    when = max(0.0, when);
-    m_endTime = when;
-}
 
-void AudioScheduledSourceNode::noteOn(double when)
-{
-    start(when);
-}
-
-void AudioScheduledSourceNode::noteOff(double when)
-{
-    stop(when);
+    if (m_stopCalled) {
+        es.throwDOMException(
+            InvalidStateError,
+            ExceptionMessages::failedToExecute(
+                "stop",
+                "OscillatorNode",
+                "cannot call stop more than once."));
+    } else if (m_playbackState == UNSCHEDULED_STATE) {
+        es.throwDOMException(
+            InvalidStateError,
+            ExceptionMessages::failedToExecute(
+                "stop",
+                "OscillatorNode",
+                "cannot call stop without calling start first."));
+    } else {
+        // This can only happen from the SCHEDULED_STATE or PLAYING_STATE. The UNSCHEDULED_STATE is
+        // handled above, and the FINISHED_STATE is only reachable after stop() has been called, and
+        // hence m_stopCalled is true. But that case is handled above.
+        when = max(0.0, when);
+        m_endTime = when;
+        m_stopCalled = true;
+    }
 }
 
 void AudioScheduledSourceNode::setOnended(PassRefPtr<EventListener> listener, DOMWrapperWorld* isolatedWorld)