Bug 517943 - Need a way to append the contents of an nsTArray to another without copying. r=benjamin, sr=dbaron.

xpcom/glue/nsTArray.h

@@ -654,6 +654,22 @@ class nsTArray : public nsTArray_base {
       return AppendElements(1);
     }
 
+    // Move all elements from another array to the end of this array without 
+    // calling copy constructors or destructors.
+    // @return A pointer to the newly appended elements, or null on OOM.
+    template<class Item>
+    elem_type *MoveElementsFrom(nsTArray<Item>& array) {
+      NS_PRECONDITION(&array != this, "argument must be different array");
+      index_type len = Length();
+      index_type otherLen = array.Length();
+      if (!EnsureCapacity(len + otherLen, sizeof(elem_type)))
+        return nsnull;
+      memcpy(Elements() + len, array.Elements(), otherLen * sizeof(elem_type));
+      IncrementLength(otherLen);      
+      array.ShiftData(0, otherLen, 0, sizeof(elem_type));
+      return Elements() + len;
+    }
+
     // This method removes a range of elements from this array.
     // @param start  The starting index of the elements to remove.
     // @param count  The number of elements to remove.