fix leak of hbitmap

skia/ext/raster_handle_allocator_win.cc

 // Copyright (c) 2017 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 <windows.h>
 #include <psapi.h>
 #include <stddef.h>
 
 #include "base/debug/gdi_debug_util_win.h"
 #include "base/memory/ptr_util.h"
 #include "base/logging.h"
 #include "base/win/win_util.h"
 #include "skia/ext/platform_canvas.h"
 #include "skia/ext/skia_utils_win.h"
 #include "third_party/skia/include/core/SkMatrix.h"
 #include "third_party/skia/include/core/SkPath.h"
 #include "third_party/skia/include/core/SkRefCnt.h"
 #include "third_party/skia/include/core/SkRect.h"
 
 namespace {
 
 static void DeleteHDCCallback(void*, void* context) {
+  DCHECK_NE(context, nullptr);
   HDC hdc = static_cast<HDC>(context);
-  HBITMAP hbitmap = static_cast<HBITMAP>(SelectObject(hdc, nullptr));
-  DeleteObject(hbitmap);
-  DeleteDC(hdc);
+
+  // We must get this before we call RestoreDC, as that will drop hbitmap and
+  // reselect the original/default bitmap.
+  HGDIOBJ hbitmap = GetCurrentObject(hdc, OBJ_BITMAP);
+  DCHECK_NE(hbitmap, nullptr);
+
+  bool success = RestoreDC(hdc, -1); // effectly performs the deselect of hbitmap
+  DCHECK(success);
+
+  // Now we are the only owner, so we can delete our bitmap
+  success = DeleteObject(hbitmap);
+  DCHECK(success);
+  success = DeleteDC(hdc);
+  DCHECK(success);
 }
 
 // Allocate the layer and fill in the fields for the Rec, or return false
 // on error.
 static bool Create(int width,
                    int height,
                    bool is_opaque,
                    HANDLE shared_section,
                    bool do_clear,
                    SkRasterHandleAllocator::Rec* rec) {
   void* pixels;
   HBITMAP hbitmap =
       skia::CreateHBitmap(width, height, is_opaque, shared_section, &pixels);
   if (!hbitmap) {
     LOG(ERROR) << "CreateHBitmap failed";
     return false;
   }
 
   size_t row_bytes = skia::PlatformCanvasStrideForWidth(width);
   if (do_clear)
     sk_bzero(pixels, row_bytes * height);
 
   HDC hdc = CreateCompatibleDC(nullptr);
   if (!hdc) {
     DeleteObject(hbitmap);
     return false;
   }
   SetGraphicsMode(hdc, GM_ADVANCED);
+
+  int saveIndex = SaveDC(hdc);  // so we can Restore in the delete callback
+  DCHECK_NE(saveIndex, 0);
+
+  // Be sure to select *after* we called SaveDC.
+  // Because we're using save/restore, we don't need to explicitly track the
+  // returned "previous" value.
   SelectObject(hdc, hbitmap);
 
   rec->fReleaseProc = DeleteHDCCallback;
   rec->fReleaseCtx = hdc;
   rec->fPixels = pixels;
   rec->fRowBytes = row_bytes;
   rec->fHandle = hdc;
   return true;
 }
 
@@ skipping 60 matching lines @@
   if (failure_type == CRASH_ON_FAILURE)
     SK_CRASH();
   return nullptr;
 }
 
 HDC GetNativeDrawingContext(SkCanvas* canvas) {
   return canvas ? static_cast<HDC>(canvas->accessTopRasterHandle()) : nullptr;
 }
 
 }  // namespace skia