Bug 865537. Part 1: Add nsRange::SetEnableGravitationOnElementRemoval to suppress 'gravitation' behavior on node removal. r=smaug

--HG--
extra : rebase_source : 3823c3a0400c80b6f22021f22195f73febd5d85e

content/base/src/nsRange.cpp

@@ -662,6 +662,11 @@ nsRange::ContentRemoved(nsIDocument* aDocument,
     gravitateEnd = true;
   }
 
+  if (!mEnableGravitationOnElementRemoval) {
+    // Do not gravitate.
+    return;
+  }
+
   if (gravitateStart || gravitateEnd) {
     DoSetRange(gravitateStart ? container : mStartParent.get(),
                gravitateStart ? aIndexInContainer : mStartOffset,

content/base/src/nsRange.h

@@ -48,6 +48,7 @@ public:
     , mInSelection(false)
     , mStartOffsetWasIncremented(false)
     , mEndOffsetWasIncremented(false)
+    , mEnableGravitationOnElementRemoval(true)
 #ifdef DEBUG
     , mAssertNextInsertOrAppendIndex(-1)
     , mAssertNextInsertOrAppendNode(nullptr)
@@ -72,6 +73,20 @@ public:
   NS_DECL_CYCLE_COLLECTING_ISUPPORTS
   NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_AMBIGUOUS(nsRange, nsIDOMRange)
 
+  /**
+   * The DOM Range spec requires that when a node is removed from its parent,
+   * and the node's subtree contains the start or end point of a range, that
+   * start or end point is moved up to where the node was removed from its
+   * parent.
+   * For some internal uses of Ranges it's useful to disable that behavior,
+   * so that a range of children within a single parent is preserved even if
+   * that parent is removed from the document tree.
+   */
+  void SetEnableGravitationOnElementRemoval(bool aEnable)
+  {
+    mEnableGravitationOnElementRemoval = aEnable;
+  }
+
   // nsIDOMRange interface
   NS_DECL_NSIDOMRANGE
   
@@ -299,6 +314,7 @@ protected:
   bool mInSelection;
   bool mStartOffsetWasIncremented;
   bool mEndOffsetWasIncremented;
+  bool mEnableGravitationOnElementRemoval;
 #ifdef DEBUG
   int32_t  mAssertNextInsertOrAppendIndex;
   nsINode* mAssertNextInsertOrAppendNode;