Speedup function profile by using a hash table instead of a linear scan

runtime/vm/profiler_service.h

Index: runtime/vm/profiler_service.h
diff --git a/runtime/vm/profiler_service.h b/runtime/vm/profiler_service.h
index 4bd64da740283b6478f04b69efff3a5f71f00fb2..7280b15fd2209346a549df17c7d5ee5fbbf3f683 100644
--- a/runtime/vm/profiler_service.h
+++ b/runtime/vm/profiler_service.h
@@ -73,8 +73,8 @@ class ProfileFunction : public ZoneAllocated {
 
   const char* Name() const;
 
-  RawFunction* function() const {
-    return function_.raw();
+  const Function* function() const {
+    return &function_;
   }
 
   intptr_t table_index() const {