Enable "extern template" under MSVC

base/logging.h

 // Copyright (c) 2012 The Chromium 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 BASE_LOGGING_H_
 #define BASE_LOGGING_H_
 
 #include <cassert>
 #include <string>
 #include <cstring>
@@ skipping 465 matching lines @@
 // be out of line, while the "Impl" code should be inline.  Caller
 // takes ownership of the returned string.
 template<class t1, class t2>
 std::string* MakeCheckOpString(const t1& v1, const t2& v2, const char* names) {
   std::ostringstream ss;
   ss << names << " (" << v1 << " vs. " << v2 << ")";
   std::string* msg = new std::string(ss.str());
   return msg;
 }
 
-// MSVC doesn't like complex extern templates and DLLs.
-#if !defined(COMPILER_MSVC)
 // Commonly used instantiations of MakeCheckOpString<>. Explicitly instantiated
 // in logging.cc.
 extern template BASE_EXPORT std::string* MakeCheckOpString<int, int>(
     const int&, const int&, const char* names);
 extern template BASE_EXPORT
 std::string* MakeCheckOpString<unsigned long, unsigned long>(
     const unsigned long&, const unsigned long&, const char* names);
 extern template BASE_EXPORT
 std::string* MakeCheckOpString<unsigned long, unsigned int>(
     const unsigned long&, const unsigned int&, const char* names);
 extern template BASE_EXPORT
 std::string* MakeCheckOpString<unsigned int, unsigned long>(
     const unsigned int&, const unsigned long&, const char* names);
 extern template BASE_EXPORT
 std::string* MakeCheckOpString<std::string, std::string>(
     const std::string&, const std::string&, const char* name);
-#endif
 
 // Helper functions for CHECK_OP macro.
 // The (int, int) specialization works around the issue that the compiler
 // will not instantiate the template version of the function on values of
 // unnamed enum type - see comment below.
 #define DEFINE_CHECK_OP_IMPL(name, op) \
   template <class t1, class t2> \
   inline std::string* Check##name##Impl(const t1& v1, const t2& v2, \
                                         const char* names) { \
     if (v1 op v2) return NULL; \
@@ skipping 375 matching lines @@
 #elif NOTIMPLEMENTED_POLICY == 5
 #define NOTIMPLEMENTED() do {\
   static bool logged_once = false;\
   LOG_IF(ERROR, !logged_once) << NOTIMPLEMENTED_MSG;\
   logged_once = true;\
 } while(0);\
 EAT_STREAM_PARAMETERS
 #endif
 
 #endif  // BASE_LOGGING_H_