Make all allocation of external arrays used for IO use the IOBuffer class

runtime/bin/io_buffer.h

Index: runtime/bin/io_buffer.h
diff --git a/runtime/bin/io_buffer.h b/runtime/bin/io_buffer.h
index c9a72877e0c74b054e3a97db163555c589410cad..69a5c09b2b6240e5bd46953a66c9664a73e5fc68 100644
--- a/runtime/bin/io_buffer.h
+++ b/runtime/bin/io_buffer.h
@@ -11,8 +11,19 @@
 
 class IOBuffer {
  public:
+  // Allocate an IO buffer dart object (of type Uint8List) backed by
+  // an external byte array.
   static Dart_Handle Allocate(intptr_t size, uint8_t **buffer);
 
+  // Allocate IO buffer storage.
+  static uint8_t* Allocate(intptr_t size);
+
+  // Function for disposing of IO buffer storage. All backing storage
+  // for IO buffers must be freed using this function.
+  static void Free(void* buffer) {
+    delete[] reinterpret_cast<uint8_t*>(buffer);
+  }
+
  private:
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(IOBuffer);