[heap] Extend mutex guards for CodeRange.

src/heap/spaces.h

Index: src/heap/spaces.h
diff --git a/src/heap/spaces.h b/src/heap/spaces.h
index b11f926fde3cf373b1144b0dc67ebc5f859c0a02..6e1750ef63a1a5a9fa51bf96fc8309a3c89c289f 100644
--- a/src/heap/spaces.h
+++ b/src/heap/spaces.h
@@ -1013,9 +1013,9 @@ class CodeRange {
     size_t size;
   };
 
-  // All access to free_list_ require to take the free_list_mutex_. GC threads
-  // may access the free_list_ concurrently to the main thread.
-  base::Mutex free_list_mutex_;
+  // The global mutex guards free_list_ and allocation_list_ as GC threads may
+  // access both lists concurrently to the main thread.
+  base::Mutex code_range_mutex_;
 
   // Freed blocks of memory are added to the free list.  When the allocation
   // list is exhausted, the free list is sorted and merged to make the new