Use Layout Opportunity Iterator to position new FC blocks.

third_party/WebKit/Source/core/layout/ng/ng_layout_opportunity_iterator.h

Index: third_party/WebKit/Source/core/layout/ng/ng_layout_opportunity_iterator.h
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_layout_opportunity_iterator.h b/third_party/WebKit/Source/core/layout/ng/ng_layout_opportunity_iterator.h
index 24e8941509ff5fa5c7aec527ebbe665032bd8489..6684f93d36e68e3f1982e20740f8c017a6d687d2 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_layout_opportunity_iterator.h
+++ b/third_party/WebKit/Source/core/layout/ng/ng_layout_opportunity_iterator.h
@@ -7,6 +7,7 @@
 
 #include "core/CoreExport.h"
 #include "core/layout/ng/ng_exclusion.h"
+#include "core/layout/ng/ng_fragment.h"
 #include "core/layout/ng/ng_layout_opportunity_tree_node.h"
 #include "platform/wtf/Vector.h"
 #include "platform/wtf/text/StringBuilder.h"
@@ -16,6 +17,13 @@ namespace blink {
 typedef NGLogicalRect NGLayoutOpportunity;
 typedef Vector<NGLayoutOpportunity> NGLayoutOpportunities;
 
+NGLayoutOpportunity FindLayoutOpportunityForFragment(
+    const NGExclusions* exclusions,
+    const NGLogicalSize& size,
+    const NGLogicalOffset& origin_point,
+    const NGBoxStrut& margins,
+    const NGFragment& fragment);
+
 class CORE_EXPORT NGLayoutOpportunityIterator final {
  public:
   // Default constructor.