Encapsulate text range provider endpoints in helper class

This CL encapsulates both |start_| and |end_| ebdpoints of
AXPlatformNodeTextRangeProviderWin into an helper class with designated
getters and setters. In the follow-up CL:2432805, we are using the
setters to execute extra logic on the new endpoints.

The encapsulation will prevent anyone from setting new endpoints without
going through the setter.

Bug: N/A
Change-Id: Ia6d56391cdd0df42c0fecc87d6e575710dfda758
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2456513
Commit-Queue: Benjamin Beaudry <benjamin.beaudry@microsoft.com>
Reviewed-by: Kurt Catti-Schmidt <kschmi@microsoft.com>
Reviewed-by: Daniel Libby <dlibby@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#815256}

ui/accessibility/platform/ax_platform_node_textprovider_win_unittest.cc

@@ -44,11 +44,11 @@ class AXPlatformNodeTextProviderTest : public AXPlatformNodeWinTest {
   }
   const AXNodePosition::AXPositionInstance& GetStart(
       const AXPlatformNodeTextRangeProviderWin* text_range) {
-    return text_range->start_;
+    return text_range->start();
   }
   const AXNodePosition::AXPositionInstance& GetEnd(
       const AXPlatformNodeTextRangeProviderWin* text_range) {
-    return text_range->end_;
+    return text_range->end();
   }
 };
 

ui/accessibility/platform/ax_platform_node_textrangeprovider_win.h

@@ -112,6 +112,8 @@ class AX_EXPORT __declspec(uuid("3071e40d-a10d-45ff-a59f-6e8e1138e2c1"))
   base::string16 GetString(int max_count,
                            size_t* appended_newlines_count = nullptr);
   AXPlatformNodeWin* owner() const;
+  const AXPositionInstance& start() const { return endpoints_.GetStart(); }
+  const AXPositionInstance& end() const { return endpoints_.GetEnd(); }
   AXPlatformNodeDelegate* GetDelegate(
       const AXPositionInstanceType* position) const;
   AXPlatformNodeDelegate* GetDelegate(const AXTreeID tree_id,
@@ -173,6 +175,9 @@ class AX_EXPORT __declspec(uuid("3071e40d-a10d-45ff-a59f-6e8e1138e2c1"))
   bool HasCaretOrSelectionInPlainTextField(
       const AXPositionInstance& position) const;
 
+  void SetStart(AXPositionInstance start);
+  void SetEnd(AXPositionInstance end);
+
   static bool TextAttributeIsArrayType(TEXTATTRIBUTEID attribute_id);
   static bool TextAttributeIsUiaReservedValue(
       const base::win::VariantVector& vector);
@@ -181,8 +186,23 @@ class AX_EXPORT __declspec(uuid("3071e40d-a10d-45ff-a59f-6e8e1138e2c1"))
       const base::win::VariantVector& vector);
 
   Microsoft::WRL::ComPtr<AXPlatformNodeWin> owner_;
-  AXPositionInstance start_;
-  AXPositionInstance end_;
+
+  class TextRangeEndpoints {
+   public:
+    TextRangeEndpoints();
+    ~TextRangeEndpoints();
+    const AXPositionInstance& GetStart() const { return start_; }
+    const AXPositionInstance& GetEnd() const { return end_; }
+    void SetStart(AXPositionInstance new_start) {
+      start_ = std::move(new_start);
+    }
+    void SetEnd(AXPositionInstance new_end) { end_ = std::move(new_end); }
+
+   private:
+    AXPositionInstance start_;
+    AXPositionInstance end_;
+  };
+  TextRangeEndpoints endpoints_;
 };
 
 }  // namespace ui

ui/accessibility/platform/ax_platform_node_textrangeprovider_win_unittest.cc

@@ -165,12 +165,12 @@ class AXPlatformNodeTextRangeProviderTest : public ui::AXPlatformNodeWinTest {
  public:
   const AXNodePosition::AXPositionInstance& GetStart(
       const AXPlatformNodeTextRangeProviderWin* text_range) {
-    return text_range->start_;
+    return text_range->start();
   }
 
   const AXNodePosition::AXPositionInstance& GetEnd(
       const AXPlatformNodeTextRangeProviderWin* text_range) {
-    return text_range->end_;
+    return text_range->end();
   }
 
   ui::AXPlatformNodeWin* GetOwner(