blink: remove TODO and replace with DCHECK

AFAICT LayoutView is always a scroll container. So, the TODOs for
dealing with infinite width/height because of overflow:visible mixed
with overflow:clip can never happen. This converts them to DCHECKs.

BUG=1087667

Change-Id: I079be338a55067d6f5b1a62e72feb58709dfbc24
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2441953Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815235}

third_party/blink/renderer/core/dom/element.cc

@@ -1290,9 +1290,9 @@ int Element::clientWidth() {
             this, DocumentUpdateReason::kJavaScript);
       }
       if (GetDocument().GetPage()->GetSettings().GetForceZeroLayoutHeight()) {
-        // TODO(sky): deal with OverflowClipRect() being infinite along an
-        // axis (because of overflow: clip and overflow:visible along the
-        // opposite axis).
+        // OverflowClipRect() may return infinite along a particular axis if
+        // |layout_view| is not a scroll-container.
+        DCHECK(layout_view->IsScrollContainer());
         return AdjustForAbsoluteZoom::AdjustLayoutUnit(
                    layout_view->OverflowClipRect(PhysicalOffset()).Width(),
                    layout_view->StyleRef())
@@ -1336,9 +1336,9 @@ int Element::clientHeight() {
             this, DocumentUpdateReason::kJavaScript);
       }
       if (GetDocument().GetPage()->GetSettings().GetForceZeroLayoutHeight()) {
-        // TODO(sky): deal with OverflowClipRect() being infinite along an
-        // axis (because of overflow: clip and overflow:visible along the
-        // opposite axis).
+        // OverflowClipRect() may return infinite along a particular axis if
+        // |layout_view| is not a scroll-container.
+        DCHECK(layout_view->IsScrollContainer());
         return AdjustForAbsoluteZoom::AdjustLayoutUnit(
                    layout_view->OverflowClipRect(PhysicalOffset()).Height(),
                    layout_view->StyleRef())