Move the end of traversing LayoutObject to SelectionPaintRange member

Instead of calculating the stop LayoutObject, compute it in 
SelectionPaintRange constructor.

This is preparation for splitting SelectionState marking and
 invalidation.

Bug: 739062
Change-Id: I97083643ca9beb010f879b5c5048d71ce1783ed8
Reviewed-on: https://chromium-review.googlesource.com/577327Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Yoichi Osato <yoichio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487789}

third_party/WebKit/Source/core/editing/LayoutSelection.cpp

@@ -42,6 +42,9 @@ SelectionPaintRange::SelectionPaintRange(LayoutObject* start_layout_object,
       end_offset_(end_offset) {
   DCHECK(start_layout_object_);
   DCHECK(end_layout_object_);
+  traverse_stop_ = end_layout_object_->ChildAt(end_offset);
+  if (!traverse_stop_)
+    traverse_stop_ = end_layout_object_->NextInPreOrderAfterChildren();
   if (start_layout_object_ != end_layout_object_)
     return;
   DCHECK_LT(start_offset_, end_offset_);
@@ -79,12 +82,8 @@ SelectionPaintRange::Iterator::Iterator(const SelectionPaintRange* range) {
     current_ = nullptr;
     return;
   }
+  range_ = range;
   current_ = range->StartLayoutObject();
-  included_end_ = range->EndLayoutObject();
-  stop_ = range->EndLayoutObject()->ChildAt(range->EndOffset());
-  if (stop_)
-    return;
-  stop_ = range->EndLayoutObject()->NextInPreOrderAfterChildren();
 }
 
 LayoutObject* SelectionPaintRange::Iterator::operator*() const {
@@ -94,9 +93,10 @@ LayoutObject* SelectionPaintRange::Iterator::operator*() const {
 
 SelectionPaintRange::Iterator& SelectionPaintRange::Iterator::operator++() {
   DCHECK(current_);
-  for (current_ = current_->NextInPreOrder(); current_ && current_ != stop_;
+  for (current_ = current_->NextInPreOrder();
+       current_ && current_ != range_->traverse_stop_;
        current_ = current_->NextInPreOrder()) {
-    if (current_ == included_end_ || current_->CanBeSelectionLeaf())
+    if (current_->CanBeSelectionLeaf())
       return *this;
   }
 

third_party/WebKit/Source/core/editing/LayoutSelection.h

@@ -57,9 +57,8 @@ class SelectionPaintRange {
     LayoutObject* operator*() const;
 
    private:
+    const SelectionPaintRange* range_;
     LayoutObject* current_;
-    const LayoutObject* included_end_;
-    const LayoutObject* stop_;
   };
   Iterator begin() const { return Iterator(this); };
   Iterator end() const { return Iterator(nullptr); };
@@ -84,6 +83,7 @@ class SelectionPaintRange {
   int start_offset_ = -1;
   LayoutObject* end_layout_object_ = nullptr;
   int end_offset_ = -1;
+  LayoutObject* traverse_stop_ = nullptr;
 };
 
 class LayoutSelection final : public GarbageCollected<LayoutSelection> {