Mojo C++ bindings: Add mojo::Array<T>::reserve()

mojo/public/cpp/bindings/array.h

Index: mojo/public/cpp/bindings/array.h
diff --git a/mojo/public/cpp/bindings/array.h b/mojo/public/cpp/bindings/array.h
index a253da1f3954eed84541177cfee46df4c17a7dfa..973aa08ab4ff7a4c137ac03d884cc6edb68da831 100644
--- a/mojo/public/cpp/bindings/array.h
+++ b/mojo/public/cpp/bindings/array.h
@@ -133,6 +133,11 @@ class Array {
   // Sets the array to empty (even if previously it was null.)
   void SetToEmpty() { resize(0); }
 
+  // Ensures the underlying storage can store up to |size| elements without
+  // performing reallocations. This works like the reserve method of
+  // |std::vector|.
+  void reserve(size_t size) { vec_.reserve(size); }
+
   // Returns a const reference to the |std::vector| managed by this class. If
   // the array is null, this will be an empty vector.
   const std::vector<T>& storage() const { return vec_; }