Fix "unused variable" warnings.

gin/wrappable_unittest.cc

Index: gin/wrappable_unittest.cc
diff --git a/gin/wrappable_unittest.cc b/gin/wrappable_unittest.cc
index e773d2d283940c2d042d5c0662c94faf9111080f..905346e64e27620ee64e0f015453879aaea37cc9 100644
--- a/gin/wrappable_unittest.cc
+++ b/gin/wrappable_unittest.cc
@@ -16,11 +16,17 @@
 
 namespace gin {
 
+// This useless base class ensures that the value of a pointer to a MyObject
+// (below) is not the same as the value of that pointer cast to the object's
+// WrappableBase base.
 class BaseClass {
  public:
   BaseClass() : value_(23) {}
   virtual ~BaseClass() {}
 
+  // So the compiler doesn't complain that |value_| is unused.
+  int value() const { return value_; }
+
  private:
   int value_;