Heap profiler: Add static assertions for heap snapshot entities' sizes.

src/profile-generator.cc

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1170 matching lines @@
     }
     edge->to()->Print(1, 0);
   }
   OS::Print("\n");
 }
 
 
 HeapObject *const HeapSnapshot::kInternalRootObject =
     reinterpret_cast<HeapObject*>(1);
 
+
+// It is very important to keep objects that form a heap snapshot
+// as small as possible.
+namespace {  // Avoid littering the global namespace.
+
+template <size_t ptr_size> struct SnapshotSizeConstants;
+
+template <> struct SnapshotSizeConstants<4> {
+  static const int kExpectedHeapGraphEdgeSize = 12;
+  static const int kExpectedHeapEntrySize = 32;
+};
+
+template <> struct SnapshotSizeConstants<8> {
+  static const int kExpectedHeapGraphEdgeSize = 24;
+  static const int kExpectedHeapEntrySize = 40;
+};
+
+}  // namespace
+
 HeapSnapshot::HeapSnapshot(HeapSnapshotsCollection* collection,
                            const char* title,
                            unsigned uid)
     : collection_(collection),
       title_(title),
       uid_(uid),
       root_entry_index_(-1),
       raw_entries_(NULL),
       entries_sorted_(false) {
+  STATIC_ASSERT(
+      sizeof(HeapGraphEdge) ==
+      SnapshotSizeConstants<sizeof(void*)>::kExpectedHeapGraphEdgeSize);
+  STATIC_ASSERT(
+      sizeof(HeapEntry) ==
+      SnapshotSizeConstants<sizeof(void*)>::kExpectedHeapEntrySize);
 }
 
 
 static void DisposeCalculatedData(HeapEntryCalculatedData* cdata) {
   cdata->Dispose();
 }
 
 HeapSnapshot::~HeapSnapshot() {
   DeleteArray(raw_entries_);
   calculated_data_.Iterate(DisposeCalculatedData);
@@ skipping 894 matching lines @@
     HeapEntry* entry = added_entries[i];
     if (entry->painted_reachable())
       diff->AddAddedEntry(add_child_index++, added_entry_index++, entry);
   }
   return diff;
 }
 
 } }  // namespace v8::internal
 
 #endif  // ENABLE_LOGGING_AND_PROFILING