Report PPAPI plugin load error code to UMA.

mojo/shell/in_process_dynamic_service_runner.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 "mojo/shell/in_process_dynamic_service_runner.h"
 
 #include "base/bind.h"
 #include "base/callback_helpers.h"
 #include "base/file_util.h"
 #include "base/logging.h"
@@ skipping 31 matching lines @@
 }
 
 void InProcessDynamicServiceRunner::Run() {
   DVLOG(2) << "Loading/running Mojo app from " << app_path_.value()
            << " in process";
 
   base::ScopedClosureRunner app_deleter(
       base::Bind(base::IgnoreResult(&base::DeleteFile), app_path_, false));
 
   do {
-    std::string load_error;
+    base::NativeLibraryLoadError load_error = 0;
     base::ScopedNativeLibrary app_library(
         base::LoadNativeLibrary(app_path_, &load_error));
     if (!app_library.is_valid()) {
       LOG(ERROR) << "Failed to load library (error: " << load_error << ")";
       break;
     }
 
     typedef MojoResult (*MojoMainFunction)(MojoHandle);
     MojoMainFunction main_function = reinterpret_cast<MojoMainFunction>(
         app_library.GetFunctionPointer("MojoMain"));
     if (!main_function) {
       LOG(ERROR) << "Entrypoint MojoMain not found";
       break;
     }
 
     // |MojoMain()| takes ownership of the service handle.
     MojoResult result = main_function(service_handle_.release().value());
     if (result < MOJO_RESULT_OK)
       LOG(ERROR) << "MojoMain returned an error: " << result;
   } while (false);
 
   app_completed_callback_.Run();
   app_completed_callback_.Reset();
 }
 
 }  // namespace shell
 }  // namespace mojo