fix leak of hbitmap

use SaveDC/RestoreDC to track the original/default hbitmap in the DC. This way we can recover the actual hbitmap using GetCurrentObject, use RestoreDC to delect it and restore the original, and then delete our hbitmap and the dc.

BUG=680971

Review-Url: https://codereview.chromium.org/2629913002
Cr-Commit-Position: refs/heads/master@{#443583}

skia/ext/raster_handle_allocator_win.cc

@@ -20,10 +20,22 @@
 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
@@ -52,6 +64,13 @@ static bool Create(int width,
     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;