Order the GL overlays above windows if possible.

content/browser/renderer_host/render_widget_host_view_mac.mm

Index: content/browser/renderer_host/render_widget_host_view_mac.mm
diff --git a/content/browser/renderer_host/render_widget_host_view_mac.mm b/content/browser/renderer_host/render_widget_host_view_mac.mm
index fb8db750f25db301108bafa1a0d1ab8870b39ea2..23e26f485f4f915a86ed5a23ed502fb9908c5d55 100644
--- a/content/browser/renderer_host/render_widget_host_view_mac.mm
+++ b/content/browser/renderer_host/render_widget_host_view_mac.mm
@@ -289,6 +289,7 @@ RenderWidgetHostViewMac::RenderWidgetHostViewMac(RenderWidgetHost* widget)
       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),
@@ -316,6 +317,10 @@ void RenderWidgetHostViewMac::SetDelegate(
   [cocoa_view_ setRWHVDelegate:delegate];
 }
 
+void RenderWidgetHostViewMac::SetAllowOverlappingViews(bool overlapping) {
+  allow_overlapping_views_ = overlapping;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 // RenderWidgetHostViewMac, RenderWidgetHostView implementation:
 
@@ -1046,8 +1051,12 @@ bool RenderWidgetHostViewMac::CompositorSwapBuffers(uint64 surface_handle,
     return true;
   }
 
-  if (!compositing_iosurface_.get())
-    compositing_iosurface_.reset(CompositingIOSurfaceMac::Create());
+  if (!compositing_iosurface_.get()) {
+    CompositingIOSurfaceMac::SurfaceOrder order = allow_overlapping_views_ ?
+        CompositingIOSurfaceMac::SURFACE_ORDER_BELOW_WINDOW :
+        CompositingIOSurfaceMac::SURFACE_ORDER_ABOVE_WINDOW;
+    compositing_iosurface_.reset(CompositingIOSurfaceMac::Create(order));
+  }
 
   if (!compositing_iosurface_.get())
     return true;
@@ -2308,15 +2317,16 @@ void RenderWidgetHostViewMac::SetTextInputActive(bool active) {
 
   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);
     }