API functions returning Promises should not throw exceptions.

Source/bindings/core/v8/ExceptionState.h

Index: Source/bindings/core/v8/ExceptionState.h
diff --git a/Source/bindings/core/v8/ExceptionState.h b/Source/bindings/core/v8/ExceptionState.h
index 5050237d22b1d82204d5793460c720c9aa6b9bc5..32fb1d5f0a7f029ce35c66c48d6b1c271bcbaf8a 100644
--- a/Source/bindings/core/v8/ExceptionState.h
+++ b/Source/bindings/core/v8/ExceptionState.h
@@ -32,6 +32,7 @@
 #define ExceptionState_h
 
 #include "bindings/core/v8/ScopedPersistent.h"
+#include "bindings/core/v8/ScriptPromise.h"
 #include "bindings/core/v8/V8ThrowException.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/text/WTFString.h"
@@ -40,6 +41,7 @@
 namespace blink {
 
 typedef int ExceptionCode;
+class ScriptState;
 
 class ExceptionState {
     WTF_MAKE_NONCOPYABLE(ExceptionState);
@@ -93,6 +95,9 @@ public:
         return true;
     }
 
+    // This method clears out the exception which |this| has.
+    ScriptPromise reject(ScriptState*);
+
     Context context() const { return m_context; }
     const char* propertyName() const { return m_propertyName; }
     const char* interfaceName() const { return m_interfaceName; }