Move a bunch of GC related files to heap/ subdirectory

src/heap/gc-tracer.cc

 // Copyright 2014 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.
 
 #include "src/v8.h"
 
-#include "src/gc-tracer.h"
+#include "src/heap/gc-tracer.h"
 
 namespace v8 {
 namespace internal {
 
 static intptr_t CountTotalHolesSize(Heap* heap) {
   intptr_t holes_size = 0;
   OldSpaces spaces(heap);
   for (OldSpace* space = spaces.next(); space != NULL; space = spaces.next()) {
     holes_size += space->Waste() + space->Available();
   }
@@ skipping 358 matching lines @@
     durations += iter->incremental_marking_duration;
     ++iter;
   }
 
   if (durations == 0.0) return 0;
 
   return static_cast<intptr_t>(bytes / durations);
 }
 }
 }  // namespace v8::internal