Remove grab-bag includes of v8.h from heap.

src/heap/gc-tracer.cc

Index: src/heap/gc-tracer.cc
diff --git a/src/heap/gc-tracer.cc b/src/heap/gc-tracer.cc
index 7dbe5fc2ee0f142a2ae88d636a1cb3bb1b3a2803..3b8e24b4743980f58d14f88c79eea07b5fe57c86 100644
--- a/src/heap/gc-tracer.cc
+++ b/src/heap/gc-tracer.cc
@@ -2,10 +2,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "src/v8.h"
-
 #include "src/heap/gc-tracer.h"
 
+#include "src/counters.h"
+#include "src/heap/heap.h"
+#include "src/isolate.h"
+#include "src/objects-inl.h"  // TODO(mstarzinger): Temporary cycle breaker!
+
 namespace v8 {
 namespace internal {