Fix crash when scrolling to the bottom of an iframe with --root-layer-scrolls

patch/patch.cfg

@@ -251,4 +251,11 @@ patches = [
     'name': 'render_view_host_impl_1392',
     'path': '../content/browser/renderer_host/',
   },
+  {
+    # Fix crash when scrolling to the bottom of an iframe with
+    # --root-layer-scrolls
+    # https://codereview.chromium.org/2150153002
+    'name': 'viewport_2150153002',
+    'path': '../',
+  },
 ]

patch/patches/viewport_2150153002.patch

@@ -0,0 +1,24 @@
+diff --git cc/layers/viewport.cc cc/layers/viewport.cc
+index d80d40c..30984592 100644
+--- cc/layers/viewport.cc
++++ cc/layers/viewport.cc
+@@ -36,6 +36,9 @@ Viewport::ScrollResult Viewport::ScrollBy(const gfx::Vector2dF& delta,
+                                           const gfx::Point& viewport_point,
+                                           bool is_direct_manipulation,
+                                           bool affect_top_controls) {
++  if (!OuterScrollLayer())
++    return ScrollResult();
++
+   gfx::Vector2dF content_delta = delta;
+ 
+   if (affect_top_controls && ShouldTopControlsConsumeScroll(delta))
+@@ -74,6 +77,9 @@ bool Viewport::ShouldAnimateViewport(const gfx::Vector2dF& viewport_delta,
+ }
+ 
+ gfx::Vector2dF Viewport::ScrollAnimated(const gfx::Vector2dF& delta) {
++  if (!OuterScrollLayer())
++    return gfx::Vector2dF(0, 0);
++
+   ScrollTree& scroll_tree =
+       host_impl_->active_tree()->property_trees()->scroll_tree;
+