include fixing: api.h shouldn't include objects-inl.h

src/handles.h

 // Copyright 2011 the V8 project 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 V8_HANDLES_H_
 #define V8_HANDLES_H_
 
 #include "include/v8.h"
 #include "src/base/functional.h"
 #include "src/base/macros.h"
@@ skipping 73 matching lines @@
 //
 // Also note that Handles do not provide default equality comparison or hashing
 // operators on purpose. Such operators would be misleading, because intended
 // semantics is ambiguous between Handle location and object identity. Instead
 // use either {is_identical_to} or {location} explicitly.
 template <typename T>
 class Handle final : public HandleBase {
  public:
   V8_INLINE explicit Handle(T** location = nullptr)
       : HandleBase(reinterpret_cast<Object**>(location)) {
-    Object* a = nullptr;
-    T* b = nullptr;
-    a = b;  // Fake assignment to enforce type checks.
-    USE(a);
+    // Type check:
+    DCHECK(T::IsObjectSubclass());

[Michael Starzinger, 2017/01/09 11:33:07]

Are we allowed to use std::is_base_of (https://chromium-cpp.appspot.com/ says
everything in <type_traits> is allowed)? I have the feeling this could be
expressed as a static assert in that case. WDYT? I am thinking along the lines
of ...

static_assert(std::is_base_of<Object, T>::value, "static type violation");

[marja, 2017/01/09 11:48:36]

Done.

   }
+
   V8_INLINE explicit Handle(T* object) : Handle(object, object->GetIsolate()) {}
   V8_INLINE Handle(T* object, Isolate* isolate) : HandleBase(object, isolate) {}
 
   // Allocate a new handle for the object, do not canonicalize.
   V8_INLINE static Handle<T> New(T* object, Isolate* isolate);
 
   // Constructor for handling automatic up casting.
   // Ex. Handle<JSFunction> can be passed when Handle<Object> is expected.
   template <typename S>
   V8_INLINE Handle(Handle<S> handle)
@@ skipping 304 matching lines @@
     next = limit = NULL;
     sealed_level = level = 0;
     canonical_scope = NULL;
   }
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HANDLES_H_