win: Remove GetModuleFromAddress, deduplicate __ImageBase code.

base/win/wrapped_window_proc.cc

Index: base/win/wrapped_window_proc.cc
diff --git a/base/win/wrapped_window_proc.cc b/base/win/wrapped_window_proc.cc
index 61b79eda8851bd02e837e6a5cfd91b2becb2f8ce..0a00996fbad1a55ab674985d310cfe5c95567a12 100644
--- a/base/win/wrapped_window_proc.cc
+++ b/base/win/wrapped_window_proc.cc
@@ -6,12 +6,25 @@
 
 #include "base/atomicops.h"
 #include "base/logging.h"
-#include "base/process/memory.h"
 
 namespace {
 
 base::win::WinProcExceptionFilter s_exception_filter = NULL;
 
+HMODULE GetModuleFromWndProc(WNDPROC window_proc) {
+  HMODULE instance = NULL;
+  // Converting a pointer-to-function to a void* is undefined behavior, but
+  // Windows (and POSIX) APIs require it to work.
+  void* address = reinterpret_cast<void*>(window_proc);
+  if (!::GetModuleHandleExA(GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS |
+                            GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT,
+                            static_cast<char*>(address),

[Will Harris, 2016/04/04 01:26:44]

why double cast, why not just reinterpret_cast<> straight from window_proc here?

Is this just to make the static_cast explicit above, for the comment?

[Nico, 2016/04/04 01:38:47]

Yes. I had this inline here, but it looked cramped with the comment in here.

+                            &instance)) {
+    NOTREACHED();
+  }
+  return instance;
+}
+
 }  // namespace.
 
 namespace base {
@@ -47,7 +60,9 @@ BASE_EXPORT void InitializeWindowClass(
   class_out->lpfnWndProc = window_proc;
   class_out->cbClsExtra = class_extra;
   class_out->cbWndExtra = window_extra;
-  class_out->hInstance = base::GetModuleFromAddress(window_proc);
+  // RegisterClassEx uses a handle of the module containing the window procedure
+  // to distinguish identically named classes registered in different modules.
+  class_out->hInstance = GetModuleFromWndProc(window_proc);
   class_out->hIcon = large_icon;
   class_out->hCursor = cursor;
   class_out->hbrBackground = background;