Expand PaintLayer clip to account for hidden URL bar with document.rootScroller

third_party/WebKit/Source/core/layout/LayoutBox.cpp

Index: third_party/WebKit/Source/core/layout/LayoutBox.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBox.cpp b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
index 3ad08c2f8690a0b53c26c12ddbb85d11157304f1..5c44b4465a5bc2e3a6b25a5c16ce75dea78fbfca 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
@@ -28,6 +28,7 @@
 
 #include "core/dom/Document.h"
 #include "core/editing/EditingUtilities.h"
+#include "core/frame/FrameHost.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
@@ -53,10 +54,13 @@
 #include "core/layout/api/LineLayoutBox.h"
 #include "core/layout/compositing/PaintLayerCompositor.h"
 #include "core/layout/shapes/ShapeOutsideInfo.h"
+#include "core/layout/svg/LayoutSVGRoot.h"
 #include "core/page/AutoscrollController.h"
 #include "core/page/Page.h"
+#include "core/page/scrolling/RootScrollerController.h"
 #include "core/page/scrolling/ScrollingCoordinator.h"
 #include "core/page/scrolling/SnapCoordinator.h"
+#include "core/page/scrolling/TopDocumentRootScrollerController.h"
 #include "core/paint/BackgroundImageGeometry.h"
 #include "core/paint/BoxPaintInvalidator.h"
 #include "core/paint/BoxPainter.h"
@@ -1379,7 +1383,11 @@ bool LayoutBox::nodeAtPoint(HitTestResult& result,
                             HitTestAction action) {
   LayoutPoint adjustedLocation = accumulatedOffset + location();
 
-  if (!isLayoutView()) {
+  if (this !=
+      document()
+          .rootScrollerController()
+          .effectiveRootScroller()
+          .layoutObject()) {
     // Check if we need to do anything at all.
     // If we have clipping, then we can't have any spillout.
     LayoutRect overflowBox =
@@ -1789,6 +1797,25 @@ PaintInvalidationReason LayoutBox::invalidatePaintIfNeeded(
 LayoutRect LayoutBox::overflowClipRect(
     const LayoutPoint& location,
     OverlayScrollbarClipBehavior overlayScrollbarClipBehavior) const {
+  // If this box is the global root scroller, it's clip rect needs to match the
+  // viewport. This might be larger than the ordinary overflow rect since hiding
+  // the URL bar can expose more content without changing the box size.
+  if (FrameHost* host = document().frameHost()) {
+    Element* globalRootScroller =
+        host->globalRootScrollerController().globalRootScroller();
+    bool applySVGViewportClip =

[chrishtr, 2017/01/21 02:06:47]

overflowClipRect is a virtual method. You can put this in
LayoutSVGRoot.

+        isSVGRoot() && toLayoutSVGRoot(this)->shouldApplyViewportClip();
+    if (!applySVGViewportClip && node() && node() == globalRootScroller) {

[chrishtr, 2017/01/21 02:06:47]

Is it possible for the rootScroller to not have a PaintLayer? Doesn't
it have to be positioned or have overflow scroll?

+      LayoutView* topView = document().topDocument().layoutView();
+      // If the view rect is empty, LayoutView::overflowClipRect will fallback
+      // to the LayoutBox implementation so prevent infinitely recursing.
+      if (!topView->viewRect().isEmpty()) {

[chrishtr, 2017/01/21 02:06:47]

How about just adjusting overflowClipRect() for LayoutBox to know
how to do this instead? And possibly remove the code from LayoutView,
since with root-layer scrolling on the view acts more like a box.

+        return topView->overflowClipRect(location,
+                                         overlayScrollbarClipBehavior);
+      }
+    }
+  }
+
   // FIXME: When overflow-clip (CSS3) is implemented, we'll obtain the property
   // here.
   LayoutRect clipRect = borderBoxRect();