Add FrameView::MarkViewportConstrainedObjectsForLayout

A minor refactoring; the method will get a couple of other callers
in subsequent patches (which I'm breaking up for digestibility).

The new condition is something that currently will never be false;
subsequent patches will cause it be false sometimes.

BUG=701575

Review-Url: https://codereview.chromium.org/2846263002
Cr-Commit-Position: refs/heads/master@{#468066}

third_party/WebKit/Source/core/frame/FrameView.cpp

@@ -1711,7 +1711,13 @@ void FrameView::ViewportSizeChanged(bool width_changed, bool height_changed) {
     }
   }
 
-  if (!HasViewportConstrainedObjects())
+  if (GetFrame().GetDocument() && !IsInPerformLayout())
+    MarkViewportConstrainedObjectsForLayout(width_changed, height_changed);
+}
+
+void FrameView::MarkViewportConstrainedObjectsForLayout(bool width_changed,
+                                                        bool height_changed) {
+  if (!HasViewportConstrainedObjects() || !(width_changed || height_changed))
     return;
 
   for (const auto& viewport_constrained_object :

third_party/WebKit/Source/core/frame/FrameView.h

@@ -228,6 +228,8 @@ class CORE_EXPORT FrameView final
   void DidUpdateElasticOverscroll();
 
   void ViewportSizeChanged(bool width_changed, bool height_changed);
+  void MarkViewportConstrainedObjectsForLayout(bool width_changed,
+                                               bool height_changed);
 
   AtomicString MediaType() const;
   void SetMediaType(const AtomicString&);