API functions returning Promises should not throw exceptions.

Source/bindings/v8/V8StringResource.h

 /*
  * Copyright (C) 2009 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 181 matching lines @@
 
         if (LIKELY(m_v8Object->IsString()))
             return true;
 
         if (LIKELY(m_v8Object->IsInt32())) {
             setString(int32ToWebCoreString(m_v8Object->Int32Value()));
             return true;
         }
 
         m_mode = DoNotExternalize;
-        v8::TryCatch block;
         m_v8Object = m_v8Object->ToString();
-        // Handle the case where an exception is thrown as part of invoking toString on the object.
-        if (block.HasCaught()) {
-            block.ReThrow();
-            return false;
-        }
-        return true;
+        // Returns false when an exception is thrown from toString.
+        return !m_v8Object.IsEmpty();

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

I double-checked and confirmed that the new code looks equivalent to the old
code. So, OK.

[yhirano, 2014/04/14 06:12:43]

Actually, layout tests show that some regressions were introduced by this change
(fast/events/before/unload-return-bad-value.html, for example).

To fix these regressions, I added v8::TryCatch to TOSTRING_* macros.
On the other hand, in toNativeArguments and toNativeArray, I use prepare()
directly and don't call ReThrow(), because they are used in async cases as well.
It is OK because all existing toNativeArguments and toNativeArray calls are
enclosed by TONATIVE_*.

     }
 
     void setString(const String& string)
     {
         m_string = string;
         m_v8Object.Clear(); // To signal that String is ready.
     }
 
     template <class StringType>
     StringType toString() const
@@ skipping 28 matching lines @@
     if (m_v8Object.IsEmpty() || m_v8Object->IsNull() || m_v8Object->IsUndefined()) {
         setString(String());
         return true;
     }
     return prepareBase();
 }
 
 } // namespace WebCore
 
 #endif // V8StringResource_h