binding: Introduces ExceptionToPromiseScope.

third_party/WebKit/Source/bindings/core/v8/GeneratedCodeHelper.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file is for functions that are used only by generated code.
 // CAUTION:
 // All functions defined in this file should be used by generated code only.
 // If you want to use them from hand-written code, please find appropriate
 // location and move them to that location.
 
 #ifndef GeneratedCodeHelper_h
 #define GeneratedCodeHelper_h
 
+#include "bindings/core/v8/ExceptionState.h"
+#include "bindings/core/v8/V8Binding.h"
 #include "core/CoreExport.h"
 #include "wtf/PassRefPtr.h"
 #include <v8.h>
 
 namespace blink {
 
+class ScriptState;
 class SerializedScriptValue;
 
 CORE_EXPORT void v8ConstructorAttributeGetter(v8::Local<v8::Name> propertyName, const v8::PropertyCallbackInfo<v8::Value>&);
 
 CORE_EXPORT v8::Local<v8::Value> v8Deserialize(v8::Isolate*, PassRefPtr<SerializedScriptValue>);
 
+// ExceptionToPromiseScope converts a possible exception to a reject promise
+// and returns the promise instead of throwing the exception.
+//
+// Promise-returning DOM operations are required to always return a promise
+// and to never throw an exception.
+// See also http://heycam.github.io/webidl/#es-operations
+class CORE_EXPORT ExceptionToPromiseScope {

[peria, 2016/09/09 02:15:24]

I prefer to contain 'Reject' in this name.

+    STACK_ALLOCATED();
+public:
+    ExceptionToPromiseScope(const v8::FunctionCallbackInfo<v8::Value>& info, ScriptState* scriptState, ExceptionState& exceptionState)

[haraken, 2016/09/09 02:01:25]

ExceptionToPromiseRejectionScope ?

+        : m_info(info)
+        , m_scriptState(scriptState)
+        , m_exceptionState(exceptionState) { }
+    ~ExceptionToPromiseScope()
+    {
+        if (!m_exceptionState.hadException())
+            return;
+
+        v8SetReturnValue(m_info, m_exceptionState.reject(m_scriptState).v8Value());
+    }
+
+private:
+    const v8::FunctionCallbackInfo<v8::Value>& m_info;
+    ScriptState* m_scriptState;
+    ExceptionState& m_exceptionState;
+};
+
 } // namespace blink
 
 #endif // GeneratedCodeHelper_h