Bug 1677635 Part 3 - Store ink overflow and scrollable overflow in se…

…parate rects in nsOverflowAreas. r=layout-reviewers,emilio

I believe we store the rects in an array so that
`NS_FOR_FRAME_OVERFLOW_TYPES` could be implemented easily. Now the macro
is removed in Part 1, we could store the rects in two separate rects for
clarity.

nsOverflowAreas' copy constructor and assignment operator are removed
because they are the same as compiler generated ones.

Differential Revision: https://phabricator.services.mozilla.com/D97234

layout/generic/ReflowOutput.h

@@ -27,25 +27,16 @@ constexpr auto AllOverflowTypes() {
 }  // namespace mozilla
 
 struct nsOverflowAreas {
- private:
-  enum nsOverflowType {
-    eInkOverflow,
-    eScrollableOverflow,
-  };
-  nsRect mRects[2];
-
  public:
   // XXX: We can remove this alias after moving nsOverflowAreas into mozilla
   // namespace.
   using OverflowType = mozilla::OverflowType;
 
-  nsRect& InkOverflow() { return mRects[eInkOverflow]; }
-  const nsRect& InkOverflow() const { return mRects[eInkOverflow]; }
+  nsRect& InkOverflow() { return mInk; }
+  const nsRect& InkOverflow() const { return mInk; }
 
-  nsRect& ScrollableOverflow() { return mRects[eScrollableOverflow]; }
-  const nsRect& ScrollableOverflow() const {
-    return mRects[eScrollableOverflow];
-  }
+  nsRect& ScrollableOverflow() { return mScrollable; }
+  const nsRect& ScrollableOverflow() const { return mScrollable; }
 
   nsRect& Overflow(OverflowType aType) {
     return aType == OverflowType::Ink ? InkOverflow() : ScrollableOverflow();
@@ -54,23 +45,10 @@ struct nsOverflowAreas {
     return aType == OverflowType::Ink ? InkOverflow() : ScrollableOverflow();
   }
 
-  nsOverflowAreas() {
-    // default-initializes to zero due to nsRect's default constructor
-  }
-
-  nsOverflowAreas(const nsRect& aInkOverflow,
-                  const nsRect& aScrollableOverflow) {
-    mRects[eInkOverflow] = aInkOverflow;
-    mRects[eScrollableOverflow] = aScrollableOverflow;
-  }
+  nsOverflowAreas() = default;
 
-  nsOverflowAreas(const nsOverflowAreas& aOther) { *this = aOther; }
-
-  nsOverflowAreas& operator=(const nsOverflowAreas& aOther) {
-    mRects[0] = aOther.mRects[0];
-    mRects[1] = aOther.mRects[1];
-    return *this;
-  }
+  nsOverflowAreas(const nsRect& aInkOverflow, const nsRect& aScrollableOverflow)
+      : mInk(aInkOverflow), mScrollable(aScrollableOverflow) {}
 
   bool operator==(const nsOverflowAreas& aOther) const {
     // Scrollable overflow is a point-set rectangle and ink overflow
@@ -90,15 +68,12 @@ struct nsOverflowAreas {
   }
 
   nsOverflowAreas& operator+=(const nsPoint& aPoint) {
-    mRects[0] += aPoint;
-    mRects[1] += aPoint;
+    mInk += aPoint;
+    mScrollable += aPoint;
     return *this;
   }
 
-  void Clear() {
-    mRects[0].SetRect(0, 0, 0, 0);
-    mRects[1].SetRect(0, 0, 0, 0);
-  }
+  void Clear() { SetAllTo(nsRect()); }
 
   // Mutates |this| by unioning both overflow areas with |aOther|.
   void UnionWith(const nsOverflowAreas& aOther);
@@ -108,6 +83,10 @@ struct nsOverflowAreas {
 
   // Mutates |this| by setting both overflow areas to |aRect|.
   void SetAllTo(const nsRect& aRect);
+
+ private:
+  nsRect mInk;
+  nsRect mScrollable;
 };
 
 /**