[blink_gc_plugin] Complain about stack-allocated classes with GC bases, but not arbitrary non-stack…

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 88c01ab174112f29f42d7f497052c9a70c44576d..10d8f41d16df2012c81c2d07d684f538854806b1 100644
--- a/tools/clang/blink_gc_plugin/tests/stack_allocated.h
+++ b/tools/clang/blink_gc_plugin/tests/stack_allocated.h
@@ -23,12 +23,6 @@ private:
     Member<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*);
@@ -36,10 +30,19 @@ private:
     StackObject m_part; // Cannot embed a stack allocated object.
 };
 
+// Cannot derive from both heap- and stack-allocated objects.
+class DerivedHeapObject : public HeapObject, public StackObject {
+};
+
+// Cannot be stack-allocated and derive from a heap-allocated object.
+class DerivedHeapObject2 : public HeapObject {
+  STACK_ALLOCATED();
+};
+
 // STACK_ALLOCATED is inherited.
 class DerivedStackObject : public StackObject {
 private:
-    AnotherStackObject m_anotherPart; // Also fine.
+    StackObject m_anotherPart; // Also fine.
 };
 
 }