Fix DCHECK failure on bots when registry key can't be opened successfully.

chrome/browser/themes/theme_service_win.cc

 // Copyright 2016 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/themes/theme_service_win.h"
 
 #include "base/bind.h"
 #include "base/win/windows_version.h"
 #include "chrome/browser/themes/theme_properties.h"
 #include "grit/theme_resources.h"
 #include "skia/ext/skia_utils_win.h"
 #include "ui/base/win/shell.h"
 
 ThemeServiceWin::ThemeServiceWin() {
   // This just checks for Windows 10 instead of calling ShouldUseDwmFrameColor()
   // because we want to monitor the frame color even when a custom frame is in
   // use, so that it will be correct if at any time the user switches to the
   // native frame.
   if (base::win::GetVersion() >= base::win::VERSION_WIN10) {
     dwm_key_.reset(new base::win::RegKey(
         HKEY_CURRENT_USER, L"SOFTWARE\\Microsoft\\Windows\\DWM", KEY_READ));
-    OnDwmKeyUpdated();
+    if (dwm_key_->Valid())
+      OnDwmKeyUpdated();
+    else
+      dwm_key_.reset();
   }
 }
 
 ThemeServiceWin::~ThemeServiceWin() {
 }
 
 bool ThemeServiceWin::ShouldUseNativeFrame() const {
   return !HasCustomImage(IDR_THEME_FRAME) && ui::win::IsAeroGlassEnabled();
 }
 
@@ skipping 25 matching lines @@
        (color_prevalence == 1) &&
        (dwm_key_->ReadValueDW(L"AccentColor", &accent_color) == ERROR_SUCCESS))
           ? skia::COLORREFToSkColor(accent_color)
           : SK_ColorWHITE;
 
   // Watch for future changes.
   if (!dwm_key_->StartWatching(base::Bind(
           &ThemeServiceWin::OnDwmKeyUpdated, base::Unretained(this))))
     dwm_key_.reset();
 }