API functions returning Promises should not throw exceptions.

Source/bindings/core/v8/V8Binding.h

Index: Source/bindings/core/v8/V8Binding.h
diff --git a/Source/bindings/core/v8/V8Binding.h b/Source/bindings/core/v8/V8Binding.h
index 14cac2abf7a8479a83b545b4f787cd7f298cb3ff..cd03efc9e5d9b034d155efe03db82440efdef37f 100644
--- a/Source/bindings/core/v8/V8Binding.h
+++ b/Source/bindings/core/v8/V8Binding.h
@@ -952,27 +952,20 @@ PassRefPtr<TraceEvent::ConvertableToTraceFormat> devToolsTraceEventData(Executio
 
 class V8RethrowTryCatchScope FINAL {
 public:
-    explicit V8RethrowTryCatchScope(v8::TryCatch& block) : m_block(block) { }
+    explicit V8RethrowTryCatchScope(v8::TryCatch& block) : m_block(block), m_isCanceled(false) { }
+    void cancel() { m_isCanceled = true; }
     ~V8RethrowTryCatchScope()
     {
-        // ReThrow() is a no-op if no exception has been caught, so always call.
-        m_block.ReThrow();
-    }
-
-private:
-    v8::TryCatch& m_block;
-};
-
-class V8ResetTryCatchScope FINAL {
-public:
-    explicit V8ResetTryCatchScope(v8::TryCatch& block) : m_block(block) { }
-    ~V8ResetTryCatchScope()
-    {
-        m_block.Reset();
+        if (!m_isCanceled) {
+            // ReThrow() is a no-op if no exception has been caught, so always
+            // call.
+            m_block.ReThrow();
+        }
     }
 
 private:
     v8::TryCatch& m_block;
+    bool m_isCanceled;
 };
 
 } // namespace blink