Refactor native extension shared library lookup.

runtime/bin/extensions_linux.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_LINUX)
 
 #include "bin/extensions.h"
 #include <dlfcn.h>  // NOLINT
 
 
 namespace dart {
 namespace bin {
 
-void* Extensions::LoadExtensionLibrary(const char* library_path,
-                                       const char* extension_name) {
-  const char* strings[] = { library_path, "/lib",
-                             extension_name, ".so", NULL };
-  char* library_file = Concatenate(strings);
-  void* lib_handle = dlopen(library_file, RTLD_LAZY);
-  free(library_file);
-  return lib_handle;
+void* Extensions::LoadExtensionLibrary(const char* library_file) {
+  return dlopen(library_file, RTLD_LAZY);
 }
 
 void* Extensions::ResolveSymbol(void* lib_handle, const char* symbol) {
   dlerror();
   void* result = dlsym(lib_handle, symbol);
   if (dlerror() != NULL) return NULL;
   return result;
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_LINUX)