Report PPAPI plugin load error code to UMA.

content/common/plugin_list_posix.cc

Index: content/common/plugin_list_posix.cc
diff --git a/content/common/plugin_list_posix.cc b/content/common/plugin_list_posix.cc
index 72a931073c41abdf3affa45bb357e78bba99cba8..e4db7d8e66c829808d1ac05216c0718ffaf40686 100644
--- a/content/common/plugin_list_posix.cc
+++ b/content/common/plugin_list_posix.cc
@@ -240,7 +240,7 @@ void UnwrapNSPluginWrapper(void **dl, base::FilePath* unwrapped_path) {
     return;
   }
 
-  std::string error;
+  base::NativeLibraryLoadError error;
   void* newdl = base::LoadNativeLibrary(path, &error);
   if (!newdl) {
     // We couldn't load the unwrapped plugin for some reason, despite
@@ -276,7 +276,7 @@ bool PluginList::ReadWebPluginInfo(const base::FilePath& filename,
     return false;
   }
 
-  std::string error;
+  base::NativeLibraryLoadError error;
   void* dl = base::LoadNativeLibrary(filename, &error);
   if (!dl) {
     LOG_IF(ERROR, PluginList::DebugPluginLoading())