Drain StoreBufferBlock into store buffer instead of iterating over it directly.

runtime/vm/store_buffer.h

Index: runtime/vm/store_buffer.h
diff --git a/runtime/vm/store_buffer.h b/runtime/vm/store_buffer.h
index bc5295874a9391c889800e747a381fda41b62d6e..f145875f8b0928c1084308f2240e3dbed53dd5fd 100644
--- a/runtime/vm/store_buffer.h
+++ b/runtime/vm/store_buffer.h
@@ -95,6 +95,7 @@ class StoreBuffer {
 
   void AddPointer(uword address);
 
+  // Drain StoreBufferBlock into deduplication sets.
   void ProcessBlock(StoreBufferBlock* block);
 
   DedupSet* DedupSets() {
@@ -105,6 +106,10 @@ class StoreBuffer {
   }
 
  private:
+  // Add pointer to deduplication sets. Returns true if the current set is full
+  // and a new set was created.
+  bool AddPointerInternal(uword address);
+
   DedupSet* dedup_sets_;
   intptr_t count_;