Mojo cpp bindings: support Clone() for structs and arrays which don't contain handles.

mojo/public/cpp/bindings/struct_ptr.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_STRUCT_PTR_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_STRUCT_PTR_H_
 
 #include <new>
 
 #include "mojo/public/cpp/environment/logging.h"
@@ skipping 49 matching lines @@
   Struct* operator->() const {
     MOJO_DCHECK(ptr_);
     return ptr_;
   }
   Struct* get() const { return ptr_; }
 
   void Swap(StructPtr* other) {
     std::swap(ptr_, other->ptr_);
   }
 
+  // Please note that calling this method will fail compilation if the value
+  // type |Struct| doesn't have a Clone() method defined (which usually means
+  // that it contains Mojo handles).
+  StructPtr Clone() const {
+    return is_null() ? StructPtr() : ptr_->Clone();
+  }
+
  private:
   typedef Struct* StructPtr::*Testable;
 
  public:
   operator Testable() const { return ptr_ ? &StructPtr::ptr_ : 0; }
 
  private:
   friend class internal::StructHelper<Struct>;
   void Initialize() {
     MOJO_DCHECK(!ptr_);
@@ skipping 45 matching lines @@
     MOJO_DCHECK(!is_null_);
     return &value_;
   }
   Struct* get() const { return &value_; }
 
   void Swap(InlinedStructPtr* other) {
     std::swap(value_, other->value_);
     std::swap(is_null_, other->is_null_);
   }
 
+  InlinedStructPtr Clone() const {
+    return is_null() ? InlinedStructPtr() : value_.Clone();
+  }
+
  private:
   typedef Struct InlinedStructPtr::*Testable;
 
  public:
   operator Testable() const { return is_null_ ? 0 : &InlinedStructPtr::value_; }
 
  private:
   friend class internal::StructHelper<Struct>;
   void Initialize() { is_null_ = false; }
 
   void Take(InlinedStructPtr* other) {
     reset();
     Swap(other);
   }
 
   mutable Struct value_;
   bool is_null_;
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_STRUCT_PTR_H_