Order the GL overlays above windows if possible.

content/browser/renderer_host/render_widget_host_view_mac.mm

 // 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/render_widget_host_view_mac.h"
 
 #include <QuartzCore/QuartzCore.h>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
@@ skipping 271 matching lines @@
 ///////////////////////////////////////////////////////////////////////////////
 // RenderWidgetHostViewMac, public:
 
 RenderWidgetHostViewMac::RenderWidgetHostViewMac(RenderWidgetHost* widget)
     : render_widget_host_(RenderWidgetHostImpl::From(widget)),
       about_to_validate_and_paint_(false),
       call_set_needs_display_in_rect_pending_(false),
       last_frame_was_accelerated_(false),
       text_input_type_(ui::TEXT_INPUT_TYPE_NONE),
       can_compose_inline_(true),
+      allow_overlapping_views_(false),
       is_loading_(false),
       is_hidden_(false),
       weak_factory_(this),
       fullscreen_parent_host_view_(NULL) {
   // |cocoa_view_| owns us and we will be deleted when |cocoa_view_|
   // goes away.  Since we autorelease it, our caller must put
   // |GetNativeView()| into the view hierarchy right after calling us.
   cocoa_view_ = [[[RenderWidgetHostViewCocoa alloc]
                   initWithRenderWidgetHostViewMac:this] autorelease];
   render_widget_host_->SetView(this);
 }
 
 RenderWidgetHostViewMac::~RenderWidgetHostViewMac() {
   AckPendingSwapBuffers();
   UnlockMouse();
   // We are owned by RenderWidgetHostViewCocoa, so if we go away before the
   // RenderWidgetHost does we need to tell it not to hold a stale pointer to
   // us.
   if (render_widget_host_)
     render_widget_host_->SetView(NULL);
 }
 
 void RenderWidgetHostViewMac::SetDelegate(
     NSObject<RenderWidgetHostViewMacDelegate>* delegate) {
   [cocoa_view_ setRWHVDelegate:delegate];
 }
 
+void RenderWidgetHostViewMac::SetAllowOverlappingViews(bool overlapping) {
+  allow_overlapping_views_ = overlapping;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 // RenderWidgetHostViewMac, RenderWidgetHostView implementation:
 
 void RenderWidgetHostViewMac::InitAsChild(
     gfx::NativeView parent_view) {
 }
 
 void RenderWidgetHostViewMac::InitAsPopup(
     RenderWidgetHostView* parent_host_view,
     const gfx::Rect& pos) {
@@ skipping 710 matching lines @@
           [NSString stringWithFormat:@"window %s delegate %s controller %s",
                     object_getClassName(window),
                     object_getClassName([window delegate]),
                     object_getClassName([window windowController])];
       base::mac::SetCrashKeyValue(kCrashKey, value);
     }
 
     return true;
   }
 
-  if (!compositing_iosurface_.get())
-    compositing_iosurface_.reset(CompositingIOSurfaceMac::Create());
+  if (!compositing_iosurface_.get()) {
+    compositing_iosurface_.reset(
+        CompositingIOSurfaceMac::Create(allow_overlapping_views_));
+  }
 
   if (!compositing_iosurface_.get())
     return true;
 
   compositing_iosurface_->SetIOSurface(surface_handle, size);
 
   GotAcceleratedFrame();
 
   gfx::Size window_size(NSSizeToCGSize([cocoa_view_ frame].size));
   if (window_size.IsEmpty()) {
@@ skipping 1240 matching lines @@
   // blit the IOSurface below.
   renderWidgetHostView_->about_to_validate_and_paint_ = true;
   BackingStoreMac* backingStore = static_cast<BackingStoreMac*>(
       renderWidgetHostView_->render_widget_host_->GetBackingStore(true));
   renderWidgetHostView_->about_to_validate_and_paint_ = false;
 
   const gfx::Rect damagedRect([self flipNSRectToRect:dirtyRect]);
 
   if (renderWidgetHostView_->last_frame_was_accelerated_ &&
       renderWidgetHostView_->compositing_iosurface_.get()) {
-    {
+    if (renderWidgetHostView_->allow_overlapping_views_) {
+      // If overlapping views need to be allowed, punch a hole in the window
+      // to expose the GL underlay.
       TRACE_EVENT2("gpu", "NSRectFill clear", "w", damagedRect.width(),
                    "h", damagedRect.height());
-      // Draw transparency to expose the GL underlay. NSRectFill is extremely
-      // slow (15ms for a window on a fast MacPro), so this is only done when
-      // it's a real invalidation from window damage (not when a BuffersSwapped
-      // was received). Note that even a 1x1 NSRectFill can take many
-      // milliseconds sometimes (!) so this is skipped completely for drawRects
-      // that are triggered by BuffersSwapped messages.
+      // NSRectFill is extremely slow (15ms for a window on a fast MacPro), so
+      // this is only done when it's a real invalidation from window damage (not
+      // when a BuffersSwapped was received). Note that even a 1x1 NSRectFill
+      // can take many milliseconds sometimes (!) so this is skipped completely
+      // for drawRects that are triggered by BuffersSwapped messages.
       [[NSColor clearColor] set];
       NSRectFill(dirtyRect);
     }
 
     renderWidgetHostView_->compositing_iosurface_->DrawIOSurface(
         self, ScaleFactor(self));
     return;
   }
 
   if (backingStore) {
@@ skipping 1035 matching lines @@
   if (!string) return NO;
 
   // If the user is currently using an IME, confirm the IME input,
   // and then insert the text from the service, the same as TextEdit and Safari.
   [self confirmComposition];
   [self insertText:string];
   return YES;
 }
 
 @end