Report PPAPI plugin load error code to UMA.

mojo/shell/app_child_process.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/app_child_process.h"
 
 #include "base/bind.h"
 #include "base/callback_helpers.h"
 #include "base/file_util.h"
 #include "base/files/file_path.h"
@@ skipping 215 matching lines @@
   static void StartAppOnMainThread(const base::FilePath& app_path,
                                    ScopedMessagePipeHandle service) {
     // TODO(vtl): This is copied from in_process_dynamic_service_runner.cc.
     DVLOG(2) << "Loading/running Mojo app from " << app_path.value()
              << " out of process";
 
     base::ScopedClosureRunner app_deleter(
         base::Bind(base::IgnoreResult(&base::DeleteFile), app_path, false));
 
     do {
-      std::string load_error;
+      base::NativeLibraryLoadError load_error;
       base::ScopedNativeLibrary app_library(
           base::LoadNativeLibrary(app_path, &load_error));
       if (!app_library.is_valid()) {
-        LOG(ERROR) << "Failed to load library (error: " << load_error << ")";
+        LOG(ERROR) << "Failed to load library (error: " << load_error.ToString()
+                   << ")";
         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;
       }
@@ skipping 41 matching lines @@
   blocker.Block();
 
   app_context.controller_runner()->PostTask(
       FROM_HERE,
       base::Bind(&AppChildControllerImpl::Shutdown,
       base::Unretained(app_context.controller())));
 }
 
 }  // namespace shell
 }  // namespace mojo