Remove MenuManager use of memtables (bug 5899 part 2, r=fyren).

public/amtl/am-string.h

@@ -104,17 +104,29 @@ class AString
     return chars()[index];
   }
 
+  void setVoid() {
+    chars_ = NULL;
+    length_ = kInvalidLength;
+  }
+
+  bool isVoid() const {
+    return length_ == kInvalidLength;
+  }
+
   size_t length() const {
+    assert(!isVoid());
     return length_;
   }
 
   const char *chars() const {
     if (!chars_)
-      return "";
+      return isVoid() ? NULL : "";
     return chars_;
   }
 
  private:
+  static const size_t kInvalidLength = (size_t)-1;
+
   void set(const char *str, size_t length) {
     chars_ = new char[length + 1];
     length_ = length;

public/amtl/am-vector.h

@@ -85,6 +85,29 @@ class Vector : public AllocPolicy
     nitems_++;
   }
 
+  // Shift all elements including |at| up by one, and insert |item| at the
+  // given position. This is a linear-time operation.
+  bool insert(size_t at, const T &item) {
+    if (!moveUp(at))
+      return false;
+    new (&data_[at]) T(item);
+    return true;
+  }
+  bool insert(size_t at, Moveable<T> item) {
+    if (!moveUp(at))
+      return false;
+    new (&data_[at]) T(item);
+    return true;
+  }
+
+  // Shift all elements at the given position down, removing the given
+  // element. This is a linear-time operation.
+  void remove(size_t at) {
+    for (size_t i = at; i < length() - 1; i++)
+      data_[i] = T(Moveable<T>(data_[i + 1]));
+    pop();
+  }
+
   T popCopy() {
     T t = at(length() - 1);
     pop();
@@ -154,6 +177,15 @@ class Vector : public AllocPolicy
     maxsize_ = 0;
   }
 
+  bool moveUp(size_t at) {
+    if (!growIfNeeded(1))
+      return false;
+    nitems_++;
+    for (size_t i = nitems_ - 1; i > at; i--)
+      data_[i] = T(Moveable<T>(data_[i - 1]));
+    return true;
+  }
+
   bool growIfNeeded(size_t needed)
   {
     if (!IsUintPtrAddSafe(nitems_, needed)) {