Introduce SelectionTemplate::IsBaseFirst()

This patch Introduces |SelectionTemplate::IsBaseFirst()| and utilize it for
|Start()| and |End()| as preparation of make |SelectionForUndoStep::From()|
faster.

Bug: 751945
Change-Id: I560c23bc6c4d72de3be3985fd6584805ac9e7da7
Reviewed-on: https://chromium-review.googlesource.com/598664Reviewed-by: Yoichi Osato <yoichio@chromium.org>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#492001}

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

@@ -14,6 +14,7 @@ SelectionTemplate<Strategy>::SelectionTemplate(const SelectionTemplate& other)
     : base_(other.base_),
       extent_(other.extent_),
       affinity_(other.affinity_),
+      direction_(other.direction_),
       is_directional_(other.is_directional_)
 #if DCHECK_IS_ON()
       ,
@@ -136,17 +137,21 @@ void SelectionTemplate<Strategy>::ShowTreeForThis() const {
 template <typename Strategy>
 const PositionTemplate<Strategy>&
 SelectionTemplate<Strategy>::ComputeEndPosition() const {
-  if (base_ == extent_)
-    return base_;
-  return base_ < extent_ ? extent_ : base_;
+  return IsBaseFirst() ? extent_ : base_;
 }
 
 template <typename Strategy>
 const PositionTemplate<Strategy>&
 SelectionTemplate<Strategy>::ComputeStartPosition() const {
-  if (base_ == extent_)
-    return base_;
-  return base_ < extent_ ? base_ : extent_;
+  return IsBaseFirst() ? base_ : extent_;
+}
+
+template <typename Strategy>
+bool SelectionTemplate<Strategy>::IsBaseFirst() const {
+  DCHECK(AssertValid());
+  if (direction_ == Direction::kNotComputed)
+    direction_ = base_ <= extent_ ? Direction::kForward : Direction::kBackward;
+  return direction_ == Direction::kForward;
 }
 
 template <typename Strategy>
@@ -201,6 +206,8 @@ template <typename Strategy>
 SelectionTemplate<Strategy> SelectionTemplate<Strategy>::Builder::Build()
     const {
   DCHECK(selection_.AssertValid());
+  selection_.direction_ =
+      selection_.IsNone() ? Direction::kForward : Direction::kNotComputed;
   return selection_;
 }
 

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

@@ -82,6 +82,7 @@ class CORE_EXPORT SelectionTemplate final {
   const PositionTemplate<Strategy>& Base() const;
   const PositionTemplate<Strategy>& Extent() const;
   TextAffinity Affinity() const { return affinity_; }
+  bool IsBaseFirst() const;
   bool IsCaret() const;
   bool IsDirectional() const { return is_directional_; }
   bool IsNone() const { return base_.IsNull(); }
@@ -108,11 +109,18 @@ class CORE_EXPORT SelectionTemplate final {
  private:
   friend class SelectionEditor;
 
+  enum class Direction {
+    kNotComputed,
+    kForward,   // base <= extent
+    kBackward,  // base > extent
+  };
+
   Document* GetDocument() const;
 
   PositionTemplate<Strategy> base_;
   PositionTemplate<Strategy> extent_;
   TextAffinity affinity_ = TextAffinity::kDownstream;
+  mutable Direction direction_ = Direction::kForward;
   bool is_directional_ = false;
 #if DCHECK_IS_ON()
   uint64_t dom_tree_version_;

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

@@ -15,12 +15,32 @@ TEST_F(SelectionTest, defaultConstructor) {
   SelectionInDOMTree selection;
 
   EXPECT_EQ(TextAffinity::kDownstream, selection.Affinity());
+  EXPECT_TRUE(selection.IsBaseFirst());
   EXPECT_FALSE(selection.IsDirectional());
   EXPECT_TRUE(selection.IsNone());
   EXPECT_EQ(Position(), selection.Base());
   EXPECT_EQ(Position(), selection.Extent());
 }
 
+TEST_F(SelectionTest, IsBaseFirst) {
+  SetBodyContent("<div id='sample'>abcdef</div>");
+
+  Element* sample = GetDocument().getElementById("sample");
+  Position base(Position(sample->firstChild(), 4));
+  Position extent(Position(sample->firstChild(), 2));
+  SelectionInDOMTree::Builder builder;
+  builder.Collapse(base);
+  builder.Extend(extent);
+  const SelectionInDOMTree& selection = builder.Build();
+
+  EXPECT_EQ(TextAffinity::kDownstream, selection.Affinity());
+  EXPECT_FALSE(selection.IsBaseFirst());
+  EXPECT_FALSE(selection.IsDirectional());
+  EXPECT_FALSE(selection.IsNone());
+  EXPECT_EQ(base, selection.Base());
+  EXPECT_EQ(extent, selection.Extent());
+}
+
 TEST_F(SelectionTest, caret) {
   SetBodyContent("<div id='sample'>abcdef</div>");
 
@@ -31,6 +51,7 @@ TEST_F(SelectionTest, caret) {
   const SelectionInDOMTree& selection = builder.Build();
 
   EXPECT_EQ(TextAffinity::kDownstream, selection.Affinity());
+  EXPECT_TRUE(selection.IsBaseFirst());
   EXPECT_FALSE(selection.IsDirectional());
   EXPECT_FALSE(selection.IsNone());
   EXPECT_EQ(position, selection.Base());
@@ -49,6 +70,7 @@ TEST_F(SelectionTest, range) {
   const SelectionInDOMTree& selection = builder.Build();
 
   EXPECT_EQ(TextAffinity::kDownstream, selection.Affinity());
+  EXPECT_TRUE(selection.IsBaseFirst());
   EXPECT_FALSE(selection.IsDirectional());
   EXPECT_FALSE(selection.IsNone());
   EXPECT_EQ(base, selection.Base());