[LayoutNG] Refactor of HandleInflow children.

This moves a bunch of code around and some additional comments.

Before the code for handling an inflow element was a little difficult to follow.
Now most of the code and complexities are inside HandleInflow. Functions which
this calls are now relatively simple.

BUG=635619

Review-Url: https://codereview.chromium.org/2975973002
Cr-Commit-Position: refs/heads/master@{#486260}

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

@@ -75,17 +75,16 @@ class CORE_EXPORT NGBlockLayoutAlgorithm
       const WTF::Optional<NGLogicalOffset> floats_bfc_offset = WTF::nullopt);
 
   // @return Estimated BFC offset for the "to be layout" child.
-  WTF::Optional<NGInflowChildData> PrepareChildLayout(
-      const NGPreviousInflowPosition&,
-      NGLayoutInputNode);
+  NGInflowChildData ComputeChildData(const NGPreviousInflowPosition&,
+                                     NGLayoutInputNode);
 
-  WTF::Optional<NGPreviousInflowPosition> FinishChildLayout(
-      const NGConstraintSpace&,
-      const NGPreviousInflowPosition& prev_data,
+  NGPreviousInflowPosition ComputeInflowPosition(
+      const NGPreviousInflowPosition& previous_inflow_position,
       const NGInflowChildData& child_data,
-      NGLayoutInputNode child,
-      NGBreakToken* child_break_token,
-      RefPtr<NGLayoutResult>);
+      const WTF::Optional<NGLogicalOffset>& child_bfc_offset,
+      const NGLogicalOffset& logical_offset,
+      const NGLayoutResult& layout_result,
+      const NGFragment& fragment);
 
   // Positions the fragment that establishes a new formatting context.
   //
@@ -134,9 +133,13 @@ class CORE_EXPORT NGBlockLayoutAlgorithm
                                  const NGInflowChildData& child_data);
 
   void HandleOutOfFlowPositioned(const NGPreviousInflowPosition&, NGBlockNode);
-  void HandleFloating(const NGPreviousInflowPosition&,
-                      NGBlockNode,
-                      NGBlockBreakToken*);
+  void HandleFloat(const NGPreviousInflowPosition&,
+                   NGBlockNode,
+                   NGBlockBreakToken*);
+  WTF::Optional<NGPreviousInflowPosition> HandleInflow(
+      const NGPreviousInflowPosition&,
+      NGLayoutInputNode child,
+      NGBreakToken* child_break_token);
 
   // Final adjustments before fragment creation. We need to prevent the
   // fragment from crossing fragmentainer boundaries, and rather create a break

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

@@ -28,9 +28,6 @@ class CORE_EXPORT NGFragment {
     return static_cast<NGWritingMode>(writing_mode_);
   }
 
-  // TODO(ikilpatrick): Remove once block layout algorithm refactoring complete.
-  explicit operator bool() { return physical_fragment_ != nullptr; }
-
   // Returns the border-box size.
   LayoutUnit InlineSize() const;
   LayoutUnit BlockSize() const;