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

tools/clang/blink_gc_plugin/tests/stack_allocated.h

Index: tools/clang/blink_gc_plugin/tests/stack_allocated.h
diff --git a/tools/clang/blink_gc_plugin/tests/stack_allocated.h b/tools/clang/blink_gc_plugin/tests/stack_allocated.h
index 8fe3241053ce9b88be142ec6dd065c9e87ca9a79..b1839b71e8ae4be0dbfd4480cd634f4ab42253da 100644
--- a/tools/clang/blink_gc_plugin/tests/stack_allocated.h
+++ b/tools/clang/blink_gc_plugin/tests/stack_allocated.h
@@ -9,7 +9,7 @@
 
 namespace WebCore {
 
-class HeapObject : public GarbageCollected<HeapObject> { };
+class HeapObject;
 
 class PartObject {
     DISALLOW_ALLOCATION();
@@ -23,6 +23,25 @@ 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