Report PPAPI plugin load error code to UMA.

ui/gl/gl_implementation_osmesa.cc

Index: ui/gl/gl_implementation_osmesa.cc
diff --git a/ui/gl/gl_implementation_osmesa.cc b/ui/gl/gl_implementation_osmesa.cc
index f090735ca849581e816f9430fae32933a7a4093c..c8ef8745b0f7bb0fd61bbb3ca6ebbe25a48aef2a 100644
--- a/ui/gl/gl_implementation_osmesa.cc
+++ b/ui/gl/gl_implementation_osmesa.cc
@@ -17,10 +17,11 @@ namespace gfx {
 
 // Load a library, printing an error message on failure.
 base::NativeLibrary LoadLibrary(const base::FilePath& filename) {
-  std::string error;
+  base::NativeLibraryLoadError error;
   base::NativeLibrary library = base::LoadNativeLibrary(filename, &error);
   if (!library) {
-    DVLOG(1) << "Failed to load " << filename.MaybeAsASCII() << ": " << error;
+    DVLOG(1) << "Failed to load " << filename.MaybeAsASCII() << ": "
+             << error.ToString();
     return NULL;
   }
   return library;