Expose IsGoogleLoggingInitialized() in public API.

Usually library does not have control of the process lifespan.
Without this function, it is impossible to init/shutdown reliably.
It has been one of the major pain points for years when using glog in libraries.

AFAIK 3 workarounds have been used previously:
1. Init without checking. This causes compatiblity issues with other libs using glog.
2. Also provide a init function in library's API. This makes API complicated and stateful, especially for libs that does not mean to stay for the entire life of process.
3. Steal the utility function in internal namespace. Does not work with msvc (due to missing dllexport) or `gcc -fvisibility=hidden`.

None of them are perfect, except for the last hack that usually works well on Linux.
0.5.0 changes default visibility to hidden and it does not work anymore.

Resolve #125

src/glog/logging.h.in

@@ -594,6 +594,8 @@ GOOGLE_GLOG_DLL_DECL void InitGoogleLogging(const char* argv0,
                                             void* prefix_callback_data = NULL);
 #endif
 
+GOOGLE_GLOG_DLL_DECL bool IsGoogleLoggingInitialized();
+
 // Shutdown google's logging library.
 GOOGLE_GLOG_DLL_DECL void ShutdownGoogleLogging();
 

src/logging.cc

@@ -2568,6 +2568,10 @@ void InitGoogleLogging(const char* argv0,
 }
 #endif
 
+bool IsGoogleLoggingInitialized() {
+  return glog_internal_namespace_::IsGoogleLoggingInitialized();
+}
+
 void ShutdownGoogleLogging() {
   glog_internal_namespace_::ShutdownGoogleLoggingUtilities();
   LogDestination::DeleteLogDestinations();