Used "= default" for constructors in AXTreeManagerMap and improved comments

TBR=dmazzoni@chromium.org, aleventhal@chromium.org

Change-Id: Ief1fff9084e42b284ec733ac344119d326fbe38b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2642633Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#846108}

ui/accessibility/ax_tree_manager.h

@@ -27,6 +27,8 @@ class AX_EXPORT AXTreeManager {
   // Returns nullptr if |node_id| is not found.
   virtual AXNode* GetNodeFromTree(const AXNode::AXID node_id) const = 0;
 
+  // Use `AddObserver` and `RemoveObserver` when you want to be notified when
+  // changes happen to an `XTree`
   virtual void AddObserver(AXTreeObserver* observer) {}
   virtual void RemoveObserver(AXTreeObserver* observer) {}
 
@@ -45,8 +47,8 @@ class AX_EXPORT AXTreeManager {
   // tree.
   virtual AXNode* GetParentNodeFromParentTreeAsAXNode() const = 0;
 
-  // Called when the tree manager is about to be removed from the tree
-  // AXTreeManagerMap.
+  // Called when the tree manager is about to be removed from the tree map,
+  // `AXTreeManagerMap`.
   virtual void WillBeRemovedFromMap() {}
 };
 

ui/accessibility/ax_tree_manager_map.cc

@@ -9,9 +9,9 @@
 
 namespace ui {
 
-AXTreeManagerMap::AXTreeManagerMap() {}
+AXTreeManagerMap::AXTreeManagerMap() = default;
 
-AXTreeManagerMap::~AXTreeManagerMap() {}
+AXTreeManagerMap::~AXTreeManagerMap() = default;
 
 // static
 AXTreeManagerMap& AXTreeManagerMap::GetInstance() {

ui/accessibility/ax_tree_manager_map.h

@@ -22,14 +22,16 @@ class AX_EXPORT AXTreeManagerMap {
  public:
   AXTreeManagerMap();
   ~AXTreeManagerMap();
+  AXTreeManagerMap(const AXTreeManagerMap& map) = delete;
+  AXTreeManagerMap& operator=(const AXTreeManagerMap& map) = delete;
 
   static AXTreeManagerMap& GetInstance();
   void AddTreeManager(AXTreeID tree_id, AXTreeManager* manager);
   void RemoveTreeManager(AXTreeID tree_id);
   AXTreeManager* GetManager(AXTreeID tree_id);
 
-  // If the child of the provided parent node exists in a separate child tree,
-  // return the tree manager for that child tree. Otherwise, return nullptr.
+  // If the child of `parent_node` exists in a separate child tree, return the
+  // tree manager for that child tree. Otherwise, return nullptr.
   AXTreeManager* GetManagerForChildTree(const AXNode& parent_node);
 
  private: