Fix GDI leak in NativeThemeWin::PaintIndirect

ui/native_theme/native_theme_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 "ui/native_theme/native_theme_win.h"
 
 #include <windows.h>
 #include <stddef.h>
 #include <uxtheme.h>
 #include <vsstyle.h>
@@ skipping 646 matching lines @@
                                    HDC destination_hdc,
                                    Part part,
                                    State state,
                                    const gfx::Rect& rect,
                                    const ExtraParams& extra) const {
   // TODO(asvitkine): This path is pretty inefficient - for each paint operation
   //                  it creates a new offscreen bitmap Skia canvas. This can
   //                  be sped up by doing it only once per part/state and
   //                  keeping a cache of the resulting bitmaps.
 
+  // Bitmap needs to be deleted together with DC (before or after).

[Peter Kasting, 2016/09/23 18:45:00]

According to docs I found on the web, an attempt to free the HBITMAP while it's
still selected into a valid DC will fail.  So the destruction order must be DC
first, then bitmap (unless we were to SelectObject() a new HBITMAP into the DC
first).

This seems to contradict the comment here.  The code here happens to get this in
the right order, but I'm worried about future misuse.

Maybe we should nuke CreateOffscreenSurface() and do it inline here.  That way
we can be very clear in the comments about the declaration order of different
things, and we won't risk others getting this wrong.

You'll want to rebase anyway to pick up the changes from
https://codereview.chromium.org/2355423002/ .

+  base::win::ScopedBitmap bitmap;
   // Create an offscreen canvas that is backed by an HDC.
   base::win::ScopedCreateDC offscreen_hdc(
-      skia::CreateOffscreenSurface(rect.width(), rect.height()));
+      skia::CreateOffscreenSurface(&bitmap, rect.width(), rect.height()));
   sk_sp<SkSurface> offscreen_surface =
       skia::MapPlatformSurface(offscreen_hdc.Get());
   DCHECK(offscreen_surface);
   SkCanvas* offscreen_canvas = offscreen_surface->getCanvas();
   DCHECK(offscreen_canvas);
 
   // Some of the Windows theme drawing operations do not write correct alpha
   // values for fully-opaque pixels; instead the pixels get alpha 0. This is
   // especially a problem on Windows XP or when using the Classic theme.
   //
@@ skipping 1382 matching lines @@
     break;
   case LAST:
     NOTREACHED();
     break;
   }
   theme_handles_[theme_name] = handle;
   return handle;
 }
 
 }  // namespace ui