Include the interface name when an uncloneable DOM wrapper is encountered.

third_party/WebKit/Source/bindings/core/v8/serialization/V8ScriptValueSerializer.cpp

Index: third_party/WebKit/Source/bindings/core/v8/serialization/V8ScriptValueSerializer.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/serialization/V8ScriptValueSerializer.cpp b/third_party/WebKit/Source/bindings/core/v8/serialization/V8ScriptValueSerializer.cpp
index 1674215d708636a7810e638e281690610b097b9d..f3ef4295bdb43861660f146f63522a91d23c3245 100644
--- a/third_party/WebKit/Source/bindings/core/v8/serialization/V8ScriptValueSerializer.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/serialization/V8ScriptValueSerializer.cpp
@@ -129,8 +129,10 @@ v8::Maybe<bool> V8ScriptValueSerializer::WriteHostObject(v8::Isolate* isolate, v
         DCHECK(!exceptionState.hadException());
         return v8::Just(true);
     }
-    if (!exceptionState.hadException())
-        exceptionState.throwDOMException(DataCloneError, "An object could not be cloned.");
+    if (!exceptionState.hadException()) {
+        String interface = wrappable->wrapperTypeInfo()->interfaceName;

[jbroman, 2016/09/20 23:48:54]

Before esprehn points it out, this does one unnecessary copy into a StringImpl
before then concatenating into another StringImpl. There isn't a very convenient
way to efficiently concatenate two const char*, unless we want to call it
explicitly, like:

WTF::StringAppend(wrappable->wrapperTypeInfo()->interfaceName, " could not be
cloned.");

But this isn't a big deal because we concatenate it to more things later on, and
there is much more expensive work in the exception throwing path anyhow.

We could (and perhaps should) at least add StringConcatenate overloads for
StringView. I've sketched it locally; I may upload that as a separate patch.

[haraken, 2016/09/20 23:50:08]

Can we use StringBuilder?

+        exceptionState.throwDOMException(DataCloneError, interface + " object could not be cloned.");

[esprehn, 2016/09/21 00:07:20]

String() + interface + " object could not be cloned."

avoids the copies. :)

+    }
     return v8::Nothing<bool>();
 }