ProcessSingleton now uses base::win::MessageWindow to create a message-only window.

base/win/message_window.cc

Index: base/win/message_window.cc
diff --git a/base/win/message_window.cc b/base/win/message_window.cc
index 8a9c2874d8990abeb1736258da6603da6dce8135..fa6381b59681d476ff541794fe6fd78cad74500d 100644
--- a/base/win/message_window.cc
+++ b/base/win/message_window.cc
@@ -4,20 +4,68 @@
 
 #include "base/win/message_window.h"
 
+#include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/process_util.h"
-#include "base/strings/string16.h"
-#include "base/strings/stringprintf.h"
 #include "base/win/wrapped_window_proc.h"
 
-const wchar_t kClassNameFormat[] = L"Chrome_MessageWindow_%p";
+const wchar_t kMessageWindowClassName[] = L"Chrome_MessageWindow";
 
 namespace base {
 namespace win {
 
-MessageWindow::MessageWindow()
+// Used along with LazyInstance to register a window class for message-only
+// windows created by MessageWindow.
+class MessageWindow::WindowClass {
+ public:
+  WindowClass();
+  ~WindowClass();
+
+  ATOM atom() { return atom_; }
+  HINSTANCE instance() { return instance_; }
+
+ private:
+  ATOM atom_;
+  HINSTANCE instance_;
+
+  DISALLOW_COPY_AND_ASSIGN(WindowClass);
+};
+
+static LazyInstance<MessageWindow::WindowClass> g_window_class =
+    LAZY_INSTANCE_INITIALIZER;
+
+MessageWindow::WindowClass::WindowClass()
     : atom_(0),
-      window_(NULL) {
+      instance_(base::GetModuleFromAddress(&MessageWindow::WindowProc)) {
+  WNDCLASSEX window_class;
+  window_class.cbSize = sizeof(window_class);
+  window_class.style = 0;
+  window_class.lpfnWndProc = &base::win::WrappedWindowProc<WindowProc>;
+  window_class.cbClsExtra = 0;
+  window_class.cbWndExtra = 0;
+  window_class.hInstance = instance_;
+  window_class.hIcon = NULL;
+  window_class.hCursor = NULL;
+  window_class.hbrBackground = NULL;
+  window_class.lpszMenuName = NULL;
+  window_class.lpszClassName = kMessageWindowClassName;
+  window_class.hIconSm = NULL;
+  atom_ = RegisterClassEx(&window_class);
+  if (atom_ == 0) {
+    LOG_GETLASTERROR(ERROR)
+        << "Failed to register the window class for a message-only window";
+  }
+}
+
+MessageWindow::WindowClass::~WindowClass() {
+  if (atom_ != 0) {
+    BOOL result = UnregisterClass(MAKEINTATOM(atom_), instance_);
+    DCHECK(result);
+  }
+}
+
+MessageWindow::MessageWindow()
+    : window_(NULL) {
 }
 
 MessageWindow::~MessageWindow() {
@@ -27,13 +75,6 @@ MessageWindow::~MessageWindow() {
     BOOL result = DestroyWindow(window_);
     DCHECK(result);
   }
-
-  if (atom_ != 0) {
-    BOOL result = UnregisterClass(
-        MAKEINTATOM(atom_),
-        base::GetModuleFromAddress(&MessageWindow::WindowProc));
-    DCHECK(result);
-  }
 }
 
 bool MessageWindow::Create(const MessageCallback& message_callback) {
@@ -45,41 +86,23 @@ bool MessageWindow::CreateNamed(const MessageCallback& message_callback,
   return DoCreate(message_callback, window_name.c_str());
 }
 
+// static
+HWND MessageWindow::FindWindow(const string16& window_name) {
+  return FindWindowEx(HWND_MESSAGE, NULL, kMessageWindowClassName,
+                      window_name.c_str());
+}
+
 bool MessageWindow::DoCreate(const MessageCallback& message_callback,
-                           const wchar_t* window_name) {
+                             const wchar_t* window_name) {
   DCHECK(CalledOnValidThread());
-  DCHECK(!atom_);
   DCHECK(message_callback_.is_null());
   DCHECK(!window_);
 
   message_callback_ = message_callback;
 
-  // Register a separate window class for each instance of |MessageWindow|.
-  string16 class_name = base::StringPrintf(kClassNameFormat, this);
-  HINSTANCE instance = base::GetModuleFromAddress(&MessageWindow::WindowProc);
-
-  WNDCLASSEX window_class;
-  window_class.cbSize = sizeof(window_class);
-  window_class.style = 0;
-  window_class.lpfnWndProc = &base::win::WrappedWindowProc<WindowProc>;
-  window_class.cbClsExtra = 0;
-  window_class.cbWndExtra = 0;
-  window_class.hInstance = instance;
-  window_class.hIcon = NULL;
-  window_class.hCursor = NULL;
-  window_class.hbrBackground = NULL;
-  window_class.lpszMenuName = NULL;
-  window_class.lpszClassName = class_name.c_str();
-  window_class.hIconSm = NULL;
-  atom_ = RegisterClassEx(&window_class);
-  if (atom_ == 0) {
-    LOG_GETLASTERROR(ERROR)
-        << "Failed to register the window class for a message-only window";
-    return false;
-  }
-
-  window_ = CreateWindow(MAKEINTATOM(atom_), window_name, 0, 0, 0, 0, 0,
-                         HWND_MESSAGE, 0, instance, this);
+  WindowClass& window_class = g_window_class.Get();
+  window_ = CreateWindow(MAKEINTATOM(window_class.atom()), window_name, 0, 0, 0,
+                         0, 0, HWND_MESSAGE, 0, window_class.instance(), this);
   if (!window_) {
     LOG_GETLASTERROR(ERROR) << "Failed to create a message-only window";
     return false;