Keep two empty lines between declarations for cpp files

src/heap-snapshot-generator.cc

Index: src/heap-snapshot-generator.cc
===================================================================
--- src/heap-snapshot-generator.cc	(revision 15486)
+++ src/heap-snapshot-generator.cc	(working copy)
@@ -465,6 +465,7 @@
   time_intervals_.Clear();
 }
 
+
 void HeapObjectsMap::UpdateHeapObjectsMap() {
   HEAP->CollectAllGarbage(Heap::kMakeHeapIterableMask,
                           "HeapSnapshotsCollection::UpdateHeapObjectsMap");
@@ -1991,6 +1992,7 @@
   embedder_queried_ = true;
 }
 
+
 void NativeObjectsExplorer::FillImplicitReferences() {
   Isolate* isolate = Isolate::Current();
   List<ImplicitRefGroup*>* groups =
@@ -2616,6 +2618,7 @@
   w->AddCharacter(hex_chars[u & 0xf]);
 }
 
+
 void HeapSnapshotJSONSerializer::SerializeString(const unsigned char* s) {
   writer_->AddCharacter('\n');
   writer_->AddCharacter('\"');