Bug 1159042 - p3. Refactor mDirtyRoots type into a class - r=dbaron

As mDirtyRoots will be accessed through a more cohesive API, this patch hides
the storage details (nsTArray) -- but provides almost the same API for now.

Differential Revision: https://phabricator.services.mozilla.com/D9489

--HG--
extra : moz-landing-system : lando

layout/base/PresShell.cpp

@@ -567,6 +567,32 @@ class MOZ_STACK_CLASS AutoPointerEventTargetUpdater final {
   nsIContent** mTargetContent;
 };
 
+void nsIPresShell::DirtyRootsList::AppendElement(nsIFrame* aFrame) {
+  mList.AppendElement(aFrame);
+}
+
+void nsIPresShell::DirtyRootsList::RemoveElement(nsIFrame* aFrame) {
+  mList.RemoveElement(aFrame);
+}
+
+void nsIPresShell::DirtyRootsList::RemoveElements(nsIFrame* aFrame) {
+  mList.RemoveElementsBy([&](nsIFrame* aRoot) { return aRoot == aFrame; });
+}
+
+void nsIPresShell::DirtyRootsList::RemoveElementAt(size_t aIndex) {
+  return mList.RemoveElementAt(aIndex);
+}
+
+void nsIPresShell::DirtyRootsList::Clear() { mList.Clear(); }
+
+bool nsIPresShell::DirtyRootsList::Contains(nsIFrame* aFrame) const {
+  return mList.Contains(aFrame);
+}
+
+bool nsIPresShell::DirtyRootsList::IsEmpty() const { return mList.IsEmpty(); }
+
+size_t nsIPresShell::DirtyRootsList::Length() const { return mList.Length(); }
+
 bool PresShell::sDisableNonTestMouseEvents = false;
 
 mozilla::LazyLogModule PresShell::gLog("PresShell");
@@ -2040,12 +2066,7 @@ void PresShell::NotifyDestroyingFrame(nsIFrame* aFrame) {
 
     mFrameConstructor->NotifyDestroyingFrame(aFrame);
 
-    for (int32_t idx = mDirtyRoots.Length(); idx;) {
-      --idx;
-      if (mDirtyRoots[idx] == aFrame) {
-        mDirtyRoots.RemoveElementAt(idx);
-      }
-    }
+    mDirtyRoots.RemoveElements(aFrame);
 
     // Remove frame properties
     aFrame->DeleteAllProperties();

layout/base/nsIPresShell.h

@@ -1741,8 +1741,28 @@ class nsIPresShell : public nsStubDocumentObserver {
   // A hash table of heap allocated weak frames.
   nsTHashtable<nsPtrHashKey<WeakFrame>> mWeakFrames;
 
+  class DirtyRootsList {
+   public:
+    void AppendElement(nsIFrame* aFrame);
+    void RemoveElement(nsIFrame* aFrame);
+    void RemoveElements(nsIFrame* aFrame);
+    void RemoveElementAt(size_t aIndex);
+    void Clear();
+    bool Contains(nsIFrame* aFrame) const;
+    bool IsEmpty() const;
+    size_t Length() const;
+    auto begin() const { return mList.begin(); }
+    auto begin() { return mList.begin(); }
+    auto end() const { return mList.end(); }
+    auto end() { return mList.end(); }
+    auto& operator[](size_t i) { return mList[i]; }
+
+   private:
+    nsTArray<nsIFrame*> mList;
+  };
+
   // Reflow roots that need to be reflowed.
-  nsTArray<nsIFrame*> mDirtyRoots;
+  DirtyRootsList mDirtyRoots;
 
 #ifdef MOZ_GECKO_PROFILER
   // These two fields capture call stacks of any changes that require a restyle