Add CHECKs to debug crash

It looks like this crashes because of a null outer viewport scroll node.
That should never happen here because we have an inner viewport scroll
node.

There's a few ways this could be going wrong:

- A ScrollNode is marked as the inner scroll node even though it wasn't
  registered as one in viewport_property_ids_
- The ScrollNode doesn't exist in the property tree even though it was
  registered.
- We're getting this bad combination from Blink.

I've turned a few DCHECKs into release CHECKs to narrow down which of
these it might be.

Bug: 1037759
Change-Id: I972582da6e18725557859063da0889d465063c77
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1981268
Commit-Queue: David Bokan <bokan@chromium.org>
Auto-Submit: David Bokan <bokan@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#728220}

cc/trees/layer_tree_host.cc

@@ -1077,9 +1077,13 @@ void LayerTreeHost::RegisterViewportPropertyIds(
   DCHECK(IsUsingLayerLists());
   viewport_property_ids_ = ids;
   // Outer viewport properties exist only if inner viewport property exists.
-  DCHECK(ids.inner_scroll != ScrollTree::kInvalidNodeId ||
-         (ids.outer_scroll == ScrollTree::kInvalidNodeId &&
-          ids.outer_clip == ClipTree::kInvalidNodeId));
+  // TODO(bokan): Temporarily make this a CHECK to debug crbug.com/1037759.
+  if (ids.inner_scroll == ScrollTree::kInvalidNodeId) {
+    CHECK_EQ(ids.outer_scroll, ScrollTree::kInvalidNodeId);
+    CHECK_EQ(ids.outer_clip, ClipTree::kInvalidNodeId);
+  } else {
+    CHECK_NE(ids.outer_scroll, ScrollTree::kInvalidNodeId);
+  }
 }
 
 Layer* LayerTreeHost::InnerViewportScrollLayerForTesting() const {

cc/trees/layer_tree_impl.cc

@@ -259,9 +259,13 @@ void LayerTreeImpl::UpdateScrollbarGeometries() {
     if (is_viewport_scrollbar) {
       gfx::SizeF viewport_bounds(bounds_size);
       if (scroll_node->scrolls_inner_viewport) {
-        DCHECK_EQ(scroll_node, InnerViewportScrollNode());
+        // TODO(bokan): Temporarily make these CHECKs to debug
+        // crbug.com/1037759.
+        CHECK_EQ(scroll_node, InnerViewportScrollNode());
         auto* outer_scroll_node = OuterViewportScrollNode();
-        DCHECK(outer_scroll_node);
+        CHECK_NE(viewport_property_ids_.outer_scroll,
+                 ScrollTree::kInvalidNodeId);
+        CHECK(outer_scroll_node);
 
         // Add offset and bounds contribution of outer viewport.
         current_offset +=