In WinAura, also kill the Metro viewer process in AttemptExit().

chrome/browser/browser_process_platform_part_aurawin.cc

 // Copyright (c) 2013 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 "chrome/browser/browser_process_platform_part_aurawin.h"
 
 #include "base/command_line.h"
+#include "base/logging.h"
+#include "base/process_util.h"
+#include "base/win/windows_version.h"
+#include "chrome/browser/browser_process.h"
 #include "chrome/browser/metro_viewer/metro_viewer_process_host_win.h"
 #include "chrome/common/chrome_switches.h"
 
 BrowserProcessPlatformPart::BrowserProcessPlatformPart() {
 }
 
 BrowserProcessPlatformPart::~BrowserProcessPlatformPart() {
 }
 
 void BrowserProcessPlatformPart::OnMetroViewerProcessTerminated() {
   metro_viewer_process_host_.reset(NULL);
 }
 
 void BrowserProcessPlatformPart::PlatformSpecificCommandLineProcessing(
     const CommandLine& command_line) {
-  if (command_line.HasSwitch(switches::kViewerConnection) &&
+  if (base::win::GetVersion() >= base::win::VERSION_WIN8 &&
+      command_line.HasSwitch(switches::kViewerConnection) &&
       !metro_viewer_process_host_.get()) {
     // Tell the metro viewer process host to connect to the given IPC channel.
     metro_viewer_process_host_.reset(
         new MetroViewerProcessHost(
             command_line.GetSwitchValueASCII(switches::kViewerConnection)));
   }
 }
+
+void BrowserProcessPlatformPart::AttemptExit() {
+  // On WinAura, the regular exit path is fine except on Win8+, where Ash might
+  // be active in Metro and won't go away even if all browsers are closed. The
+  // viewer process, whose host holds a reference to g_browser_process, needs to
+  // be killed as well.
+  BrowserProcessPlatformPartBase::AttemptExit();
+
+  if (base::win::GetVersion() >= base::win::VERSION_WIN8 &&
+      metro_viewer_process_host_) {
+    base::ProcessId viewer_id =
+        metro_viewer_process_host_->GetViewerProcessId();
+    if (viewer_id == base::kNullProcessId)
+      return;
+    // The viewer doesn't hold any state so it is fine to kill it before it
+    // cleanly exits. This will trigger MetroViewerProcessHost::OnChannelError()
+    // which will cleanup references to g_browser_process.
+    bool success = base::KillProcessById(viewer_id, 0, true);
+    DCHECK(success);
+  }
+}