[heap] Enforce coding style decl order in {Heap} round #1.

Order is now:
 - forward declarations
 - enums
 - nested classes
 - static consts
 - constructors
 - static methods
 - regular methods
 - members fields

Bonus:
 - Allocate*() methods are grouped together
 - Sections

BUG=

Review URL: https://codereview.chromium.org/1312503004

Cr-Commit-Position: refs/heads/master@{#30327}

src/heap/gc-tracer.cc

@@ -472,9 +472,9 @@ void GCTracer::PrintNVP() const {
   intptr_t allocated_since_last_gc =
       current_.start_object_size - previous_.end_object_size;
   PrintF("allocated=%" V8_PTR_PREFIX "d ", allocated_since_last_gc);
-  PrintF("promoted=%" V8_PTR_PREFIX "d ", heap_->promoted_objects_size_);
+  PrintF("promoted=%" V8_PTR_PREFIX "d ", heap_->promoted_objects_size());
   PrintF("semi_space_copied=%" V8_PTR_PREFIX "d ",
-         heap_->semi_space_copied_object_size_);
+         heap_->semi_space_copied_object_size());
   PrintF("nodes_died_in_new=%d ", heap_->nodes_died_in_new_space_);
   PrintF("nodes_copied_in_new=%d ", heap_->nodes_copied_in_new_space_);
   PrintF("nodes_promoted=%d ", heap_->nodes_promoted_);