API functions returning Promises should not throw exceptions.

Source/bindings/v8/ExceptionState.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 14 matching lines @@
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef ExceptionState_h
 #define ExceptionState_h
 
 #include "bindings/v8/ScopedPersistent.h"
+#include "bindings/v8/ScriptPromise.h"
 #include "bindings/v8/V8ThrowException.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/text/WTFString.h"
 #include <v8.h>
 
 namespace WebCore {
 
 typedef int ExceptionCode;
 
 class ExceptionState {
@@ skipping 40 matching lines @@
     const String& message() const { return m_message; }
 
     bool throwIfNeeded()
     {
         if (!hadException())
             return false;
         throwException();
         return true;
     }
 
+    ScriptPromise reject()
+    {
+        if (hadException())
+            return ScriptPromise::reject(m_exception.newLocal(m_isolate), m_isolate);
+        return ScriptPromise::reject(V8ThrowException::createError(v8GeneralError, "Unknown Error", m_isolate), m_isolate);

[haraken, 2014/04/11 13:57:13]

Is this behavior speced? Which should we use, v8GeneralError or DOMError?

[yhirano, 2014/04/14 01:03:37]

Domenic says[1] DOMException is more preferable than DOMError.

1:
https://github.com/domenic/promises-unwrapping/blob/master/docs/writing-speci...

+    }
+
     Context context() const { return m_context; }
     const char* propertyName() const { return m_propertyName; }
     const char* interfaceName() const { return m_interfaceName; }
 
     void rethrowV8Exception(v8::Handle<v8::Value> value)
     {
         setException(value);
     }
 
 protected:
@@ skipping 28 matching lines @@
 public:
     TrackExceptionState(): ExceptionState(ExceptionState::UnknownContext, 0, 0, v8::Handle<v8::Object>(), v8::Isolate::GetCurrent()) { }
     virtual void throwDOMException(const ExceptionCode&, const String& message) OVERRIDE;
     virtual void throwTypeError(const String& message = String()) OVERRIDE;
     virtual void throwSecurityError(const String& sanitizedMessage, const String& unsanitizedMessage = String()) OVERRIDE;
 };
 
 } // namespace WebCore
 
 #endif // ExceptionState_h