Bug 1361301: Add nsContentUtils::GetCommonFlattenedTreeAncestor. r=smaug

MozReview-Commit-ID: EVyjTrjpid2

--HG--
extra : rebase_source : 7f0933c88b78275682be96f3ea596bfb24ec9aa4

dom/base/nsContentUtils.cpp

@@ -2547,6 +2547,16 @@ nsContentUtils::GetCommonAncestor(nsINode* aNode1, nsINode* aNode2)
   });
 }
 
+/* static */
+nsIContent*
+nsContentUtils::GetCommonFlattenedTreeAncestor(nsIContent* aContent1,
+                                               nsIContent* aContent2)
+{
+  return GetCommonAncestorInternal(aContent1, aContent2, [](nsIContent* aContent) {
+    return aContent->GetFlattenedTreeParent();
+  });
+}
+
 /* static */
 bool
 nsContentUtils::PositionIsBefore(nsINode* aNode1, nsINode* aNode2)

dom/base/nsContentUtils.h

@@ -372,6 +372,12 @@ public:
    */
   static nsINode* GetCommonAncestor(nsINode* aNode1, nsINode* aNode2);
 
+  /**
+   * Returns the common flattened tree ancestor, if any, for two given content
+   * nodes.
+   */
+  static nsIContent* GetCommonFlattenedTreeAncestor(nsIContent* aContent1,
+                                                    nsIContent* aContent2);
 
   /**
    * Returns true if aNode1 is before aNode2 in the same connected

dom/events/EventStateManager.cpp

@@ -4776,48 +4776,13 @@ GetLabelTarget(nsIContent* aPossibleLabel)
   return label->GetLabeledElement();
 }
 
-static nsIContent* FindCommonAncestor(nsIContent *aNode1, nsIContent *aNode2)
+static nsIContent*
+FindCommonAncestor(nsIContent* aNode1, nsIContent* aNode2)
 {
-  // Find closest common ancestor
-  if (aNode1 && aNode2) {
-    // Find the nearest common ancestor by counting the distance to the
-    // root and then walking up again, in pairs.
-    int32_t offset = 0;
-    nsIContent *anc1 = aNode1;
-    for (;;) {
-      ++offset;
-      nsIContent* parent = anc1->GetFlattenedTreeParent();
-      if (!parent)
-        break;
-      anc1 = parent;
-    }
-    nsIContent *anc2 = aNode2;
-    for (;;) {
-      --offset;
-      nsIContent* parent = anc2->GetFlattenedTreeParent();
-      if (!parent)
-        break;
-      anc2 = parent;
-    }
-    if (anc1 == anc2) {
-      anc1 = aNode1;
-      anc2 = aNode2;
-      while (offset > 0) {
-        anc1 = anc1->GetFlattenedTreeParent();
-        --offset;
-      }
-      while (offset < 0) {
-        anc2 = anc2->GetFlattenedTreeParent();
-        ++offset;
-      }
-      while (anc1 != anc2) {
-        anc1 = anc1->GetFlattenedTreeParent();
-        anc2 = anc2->GetFlattenedTreeParent();
-      }
-      return anc1;
-    }
+  if (!aNode1 || !aNode2) {
+    return nullptr;
   }
-  return nullptr;
+  return nsContentUtils::GetCommonFlattenedTreeAncestor(aNode1, aNode2);
 }
 
 /* static */