Issue 6526 - *ToV8String() return MaybeLocal<> and check Call() return value

src/Utils.h

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 38 matching lines @@
       if (value.IsEmpty())
         throw AdblockPlus::JsError("Empty value at ", filename, line);
       return value.ToLocalChecked();
     }
 
 #define CHECKED_TO_LOCAL(isolate, value, tryCatch)                      \
     AdblockPlus::Utils::CheckedToLocal(isolate, value, tryCatch, __FILE__, __LINE__)
 
     std::string FromV8String(v8::Isolate* isolate, const v8::Local<v8::Value>& value);
     StringBuffer StringBufferFromV8String(v8::Isolate* isolate, const v8::Local<v8::Value>& value);
-    v8::Local<v8::String> ToV8String(v8::Isolate* isolate, const std::string& str);
-    v8::Local<v8::String> StringBufferToV8String(v8::Isolate* isolate, const StringBuffer& bytes);
+    v8::MaybeLocal<v8::String> ToV8String(v8::Isolate* isolate, const std::string& str);
+    v8::MaybeLocal<v8::String> StringBufferToV8String(v8::Isolate* isolate, const StringBuffer& bytes);
     void ThrowExceptionInJS(v8::Isolate* isolate, const std::string& str);
 
     // Code for templated function has to be in a header file, can't be in .cpp
     template<class T>
     T TrimString(const T& text)
     {
       // Via http://stackoverflow.com/questions/216823/whats-the-best-way-to-trim-stdstring
       T trimmed(text);
       trimmed.erase(trimmed.begin(), std::find_if(trimmed.begin(), trimmed.end(), std::not1(std::ptr_fun<int, int>(std::isspace))));
       trimmed.erase(std::find_if(trimmed.rbegin(), trimmed.rend(), std::not1(std::ptr_fun<int, int>(std::isspace))).base(), trimmed.end());
       return trimmed;
     }
 #ifdef _WIN32
     std::wstring ToUtf16String(const std::string& str);
     std::string ToUtf8String(const std::wstring& str);
     std::wstring CanonizeUrl(const std::wstring& url);
 #endif
   }
 }
 
 #endif