Add dump_symbol_stats to dump symbol table stats at the end of a test run

vm/symbols.h

Index: vm/symbols.h
===================================================================
--- vm/symbols.h	(revision 15988)
+++ vm/symbols.h	(working copy)
@@ -226,10 +226,12 @@
 
   static bool IsPredefinedHandle(uword address);
 
+  static void DumpStats();
+
  private:
   enum {
-    kInitialVMIsolateSymtabSize = ((kMaxId + 15) & -16),
-    kInitialSymtabSize = 256
+    kInitialVMIsolateSymtabSize = 512,
+    kInitialSymtabSize = 2048
   };
 
   // Helper functions to create a symbol given a string or set of characters.
@@ -275,6 +277,11 @@
   // stored in the vm isolate.
   static VMHandles predefined_handles_;
 
+  // Statistics used to measure the efficiency of the symbol table.
+  static const intptr_t kMaxCollisionBuckets = 10;
+  static intptr_t num_of_grows_;
+  static intptr_t collision_count_[kMaxCollisionBuckets];
+
 #define DECLARE_SYMBOL_HANDLE(symbol)                                          \
   static String* symbol##_handle_;
 PREDEFINED_SYMBOL_HANDLES_LIST(DECLARE_SYMBOL_HANDLE)