Add checks for stack-allocated types and their uses in fields.

tools/clang/blink_gc_plugin/tests/stack_allocated.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 STACK_ALLOCATED_H_
 #define STACK_ALLOCATED_H_
 
 #include "heap/stubs.h"
 
 namespace WebCore {
 
-class HeapObject : public GarbageCollected<HeapObject> { };
+class HeapObject;
 
 class PartObject {
     DISALLOW_ALLOCATION();
 private:
     Member<HeapObject> m_obj; // Needs tracing.
 };
 
 class StackObject {
     STACK_ALLOCATED();
 private:
     HeapObject* m_obj; // Does not need tracing.
 };
 
+class AnotherStackObject : public PartObject { // Invalid base.
+    STACK_ALLOCATED();
+private:
+    StackObject m_part; // Can embed a stack allocated object.
+};
+
+class HeapObject : public GarbageCollected<HeapObject> {
+public:
+    void trace(Visitor*);
+private:
+    StackObject m_part; // Cannot embed a stack allocated object.
+};
+
+// STACK_ALLOCATED is inherited.
+class DerivedStackObject : public StackObject {
+private:
+    AnotherStackObject m_anotherPart; // Also fine.
+};
+
 }
 
 #endif