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

chrome/browser/browser_process_impl_win.cc

 // Copyright (c) 2012 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_impl.h"
 
 #include "base/command_line.h"
-#include "chrome/common/chrome_switches.h"
 
 #if defined(USE_AURA)
+#include "base/logging.h"
+#include "base/process_util.h"
 #include "chrome/browser/metro_viewer/metro_viewer_process_host_win.h"
+#include "chrome/common/chrome_switches.h"
 #endif
 
 void BrowserProcessImpl::PlatformSpecificCommandLineProcessing(
     const CommandLine& command_line) {
 #if defined(USE_AURA)
   PerformInitForWindowsAura(command_line);
 #endif
 }
 
 #if defined(USE_AURA)
 void BrowserProcessImpl::OnMetroViewerProcessTerminated() {
   metro_viewer_process_host_.reset(NULL);
 }
 
+void BrowserProcessImpl::TerminateMetroViewerProcess() {
+  if (metro_viewer_process_host_) {
+    base::ProcessId viewer_id =
+        metro_viewer_process_host_->GetViewerProcessId();
+    if (viewer_id == base::kNullProcessId) {
+      // If a |metro_viewer_process_host_| exists, it should always be connected
+      // at this point.
+      NOTREACHED();

[robertshield, 2013/05/10 16:51:48]

what if this gets called twice before OnMetroViewerProcessTerminated gets
called? Would this not then be expected?

[gab, 2013/05/13 17:46:16]

OnMetroViewerProcessTerminated() is called synchronously from OnChannelError()
so I'd guess that it's not possible for the IPC to be disconnected yet for this
to be called when metro_viewer_process_host_ is non-NULL.

Plus this method is really only meant to be called once from AttemptExit() which
is probably also not meant to be called multiple times in a short timespan.

+      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.
+    base::KillProcessById(viewer_id, 0, true);
+  }
+}
+
 void BrowserProcessImpl::PerformInitForWindowsAura(
     const CommandLine& command_line) {
   if (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)));
   }
 }
 #endif