Fix backing store scrolling on Windows in high-DPI mode.

content/browser/renderer_host/backing_store_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 "content/browser/renderer_host/backing_store_win.h"
 
 #include "base/command_line.h"
 #include "content/browser/renderer_host/render_process_host_impl.h"
 #include "content/browser/renderer_host/render_widget_host_impl.h"
 #include "content/public/common/content_switches.h"
@@ skipping 174 matching lines @@
          hdc(), rect.x(), rect.y(), SRCCOPY);
   return true;
 }
 
 void BackingStoreWin::ScrollBackingStore(const gfx::Vector2d& delta,
                                          const gfx::Rect& clip_rect,
                                          const gfx::Size& view_size) {
   // TODO(darin): this doesn't work if delta x() and y() are both non-zero!
   DCHECK(delta.x() == 0 || delta.y() == 0);
 
-  RECT damaged_rect, r = clip_rect.ToRECT();
-  ScrollDC(hdc_, delta.x(), delta.y(), NULL, &r, NULL, &damaged_rect);
+  float scale = ui::win::GetDeviceScaleFactor();
+  gfx::Rect screen_rect = gfx::ToEnclosingRect(
+      gfx::ScaleRect(clip_rect, scale));
+  int dx = static_cast<int>(delta.x() * scale);
+  int dy = static_cast<int>(delta.y() * scale);
+  RECT damaged_rect, r = screen_rect.ToRECT();
+  ScrollDC(hdc_, dx, dy, NULL, &r, NULL, &damaged_rect);
 }
 
 }  // namespace content