[inspector] provide more usefull error message for non serializable value

src/inspector/StringUtil.h

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_INSPECTOR_STRINGUTIL_H_
 #define V8_INSPECTOR_STRINGUTIL_H_
 
 #include "src/inspector/Allocator.h"
 #include "src/inspector/String16.h"
 
@@ skipping 19 matching lines @@
   static void builderReserve(StringBuilder& builder, unsigned capacity) {
     builder.reserveCapacity(capacity);
   }
 };
 
 std::unique_ptr<protocol::Value> parseJSON(const StringView& json);
 std::unique_ptr<protocol::Value> parseJSON(const String16& json);
 
 }  // namespace protocol
 
-std::unique_ptr<protocol::Value> toProtocolValue(v8::Local<v8::Context>,
+std::unique_ptr<protocol::Value> toProtocolValue(protocol::String* errorString,
+                                                 v8::Local<v8::Context>,
                                                  v8::Local<v8::Value>,
                                                  int maxDepth = 1000);
 
 v8::Local<v8::String> toV8String(v8::Isolate*, const String16&);
 v8::Local<v8::String> toV8StringInternalized(v8::Isolate*, const String16&);
 v8::Local<v8::String> toV8StringInternalized(v8::Isolate*, const char*);
 v8::Local<v8::String> toV8String(v8::Isolate*, const StringView&);
 // TODO(dgozman): rename to toString16.
 String16 toProtocolString(v8::Local<v8::String>);
 String16 toProtocolStringWithTypeCheck(v8::Local<v8::Value>);
@@ skipping 11 matching lines @@
 
  private:
   explicit StringBufferImpl(String16&);
   String16 m_owner;
   StringView m_string;
 };
 
 }  //  namespace v8_inspector
 
 #endif  // V8_INSPECTOR_STRINGUTIL_H_