ImVector: Added a const

TODO.txt

@@ -75,6 +75,7 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - layout: more generic alignment state (left/right/centered) for single items?
  - layout: clean up the InputFloatN/SliderFloatN/ColorEdit4 layout code. item width should include frame padding.
  - layout: BeginGroup() needs a border option.
+ - layout: vertical alignement of mixed height items (e.g. buttons) within a same line (#1284)
  
  - columns: sizing policy (e.g. for each column: fixed size, %, fill, distribute default size among fills) (#513, #125)
  - columns: add a conditional parameter to SetColumnOffset() (#513, #125)

imgui.h

@@ -903,7 +903,7 @@ public:
     inline const value_type&    back() const                    { IM_ASSERT(Size > 0); return Data[Size-1]; }
     inline void                 swap(ImVector<T>& rhs)          { int rhs_size = rhs.Size; rhs.Size = Size; Size = rhs_size; int rhs_cap = rhs.Capacity; rhs.Capacity = Capacity; Capacity = rhs_cap; value_type* rhs_data = rhs.Data; rhs.Data = Data; Data = rhs_data; }
 
-    inline int                  _grow_capacity(int new_size)    { int new_capacity = Capacity ? (Capacity + Capacity/2) : 8; return new_capacity > new_size ? new_capacity : new_size; }
+    inline int                  _grow_capacity(int size) const  { int new_capacity = Capacity ? (Capacity + Capacity/2) : 8; return new_capacity > size ? new_capacity : size; }
 
     inline void                 resize(int new_size)            { if (new_size > Capacity) reserve(_grow_capacity(new_size)); Size = new_size; }
     inline void                 reserve(int new_capacity)