Report PPAPI plugin load error code to UMA.

ui/gl/gl_implementation_osmesa.cc

 // Copyright 2014 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.
 
 #include "ui/gl/gl_implementation_osmesa.h"
 
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/native_library.h"
 #include "base/path_service.h"
 #include "ui/gl/gl_bindings.h"
 #include "ui/gl/gl_gl_api_implementation.h"
 #include "ui/gl/gl_implementation.h"
 #include "ui/gl/gl_osmesa_api_implementation.h"
 
 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;
 }
 
 base::NativeLibrary LoadLibrary(const char* filename) {
   return LoadLibrary(base::FilePath(filename));
 }
 
 bool InitializeStaticGLBindingsOSMesaGL() {
@@ skipping 23 matching lines @@
   SetGLGetProcAddressProc(get_proc_address);
   AddGLNativeLibrary(library);
   SetGLImplementation(kGLImplementationOSMesaGL);
 
   InitializeStaticGLBindingsGL();
   InitializeStaticGLBindingsOSMESA();
   return true;
 }
 
 }  // namespace gfx