Avoid calling RWHVWin::GetBackingStore when accelerated compositing is enabled.

content/browser/renderer_host/render_widget_host_view_win.cc

Index: content/browser/renderer_host/render_widget_host_view_win.cc
===================================================================
--- content/browser/renderer_host/render_widget_host_view_win.cc	(revision 157794)
+++ content/browser/renderer_host/render_widget_host_view_win.cc	(working copy)
@@ -1311,14 +1311,18 @@
 
   DCHECK(render_widget_host_->GetProcess()->HasConnection());
 
+  // Grab the region to paint before creation of paint_dc since it clears the
+  // damage region.
+  base::win::ScopedGDIObject<HRGN> damage_region(CreateRectRgn(0, 0, 0, 0));

[apatrick_chromium, 2012/09/20 22:14:17]

This has to be above the definition of paint_dc as the comment says.

+  GetUpdateRgn(damage_region, FALSE);
+
+  CPaintDC paint_dc(m_hWnd);

[apatrick_chromium, 2012/09/20 22:14:17]

This moved up so everything uses a single definition of paint_dc.

+
   // If the GPU process is rendering to a child window, compositing is
   // already triggered by damage to compositor_host_window_, so all we need to
   // do here is clear borders during resize.
   if (compositor_host_window_ &&
       render_widget_host_->is_accelerated_compositing_active()) {
-    // We initialize paint_dc here so that BeginPaint()/EndPaint()
-    // get called to validate the region.
-    CPaintDC paint_dc(m_hWnd);
     RECT host_rect, child_rect;
     GetClientRect(&host_rect);
     if (::GetClientRect(compositor_host_window_, &child_rect) &&
@@ -1330,6 +1334,12 @@
     return;
   }
 
+  if (accelerated_surface_.get() &&

[apatrick_chromium, 2012/09/20 22:14:17]

And this moved above the call to GetBackingStore.

+      render_widget_host_->is_accelerated_compositing_active()) {
+    AcceleratedPaint(paint_dc.m_hDC);
+    return;
+  }
+
   about_to_validate_and_paint_ = true;
   BackingStoreWin* backing_store = static_cast<BackingStoreWin*>(
       render_widget_host_->GetBackingStore(true));
@@ -1339,28 +1349,15 @@
   // changes and repaint them.
   about_to_validate_and_paint_ = false;
 
-  // Grab the region to paint before creation of paint_dc since it clears the
-  // damage region.
-  base::win::ScopedGDIObject<HRGN> damage_region(CreateRectRgn(0, 0, 0, 0));
-  GetUpdateRgn(damage_region, FALSE);
-
   if (compositor_host_window_ && hide_compositor_window_at_next_paint_) {
     ::ShowWindow(compositor_host_window_, SW_HIDE);
     hide_compositor_window_at_next_paint_ = false;
   }
 
-  CPaintDC paint_dc(m_hWnd);
-
   gfx::Rect damaged_rect(paint_dc.m_ps.rcPaint);
   if (damaged_rect.IsEmpty())
     return;
 
-  if (accelerated_surface_.get() &&
-      render_widget_host_->is_accelerated_compositing_active()) {
-    AcceleratedPaint(paint_dc.m_hDC);
-    return;
-  }
-
   if (backing_store) {
     gfx::Rect bitmap_rect(gfx::Point(), backing_store->size());