Verify that GC can handle trailing fillers in large pages.

runtime/vm/pages.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/pages.h"
 
 #include "platform/assert.h"
 #include "vm/compiler_stats.h"
 #include "vm/gc_marker.h"
 #include "vm/gc_sweeper.h"
@@ skipping 157 matching lines @@
   return page;
 }
 
 
 HeapPage* PageSpace::AllocateLargePage(intptr_t size, HeapPage::PageType type) {
   intptr_t page_size_in_words = LargePageSizeInWordsFor(size);
   HeapPage* page = HeapPage::Allocate(page_size_in_words, type);
   page->set_next(large_pages_);
   large_pages_ = page;
   usage_.capacity_in_words += page_size_in_words;
-  // Only one object in this page.
+  // Only one object in this page (at least until String::MakeExternal or
+  // Array::MakeArray is called).
   page->set_object_end(page->object_start() + size);
   return page;
 }
 
 
 void PageSpace::FreePage(HeapPage* page, HeapPage* previous_page) {
   usage_.capacity_in_words -= (page->memory_->size() >> kWordSizeLog2);
   // Remove the page from the list.
   if (previous_page != NULL) {
     previous_page->set_next(page->next());
@@ skipping 492 matching lines @@
     return 0;
   } else {
     ASSERT(total_time >= gc_time);
     int result= static_cast<int>((static_cast<double>(gc_time) /
                              static_cast<double>(total_time)) * 100);
     return result;
   }
 }
 
 }  // namespace dart