API functions returning Promises should not throw exceptions.

Source/bindings/v8/V8StringResource.h

Index: Source/bindings/v8/V8StringResource.h
diff --git a/Source/bindings/v8/V8StringResource.h b/Source/bindings/v8/V8StringResource.h
index feb63a990952c79ad04828cd77fe693c67edb140..9869cc8f2987ae0d3aa3bf68b3e07df5a84e0bd7 100644
--- a/Source/bindings/v8/V8StringResource.h
+++ b/Source/bindings/v8/V8StringResource.h
@@ -199,14 +199,9 @@ private:
         }
 
         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)