Add --dump-megamorphic-stats. Lower megamorphic cache load factor to 50%.

runtime/vm/flag_list.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_FLAG_LIST_H_
 #define VM_FLAG_LIST_H_
 
 // Don't use USING_DBC outside of this file.
 #if defined(TARGET_ARCH_DBC)
 #define USING_DBC true
@@ skipping 43 matching lines @@
 C(deoptimize_alot, false, false, bool, false,                                  \
   "Deoptimizes we are about to return to Dart code from native entries.")      \
 C(deoptimize_every, 0, 0, int, 0,                                              \
   "Deoptimize on every N stack overflow checks")                               \
 R(disable_alloc_stubs_after_gc, false, bool, false,                            \
   "Stress testing flag.")                                                      \
 R(disassemble, false, bool, false,                                             \
   "Disassemble dart code.")                                                    \
 R(disassemble_optimized, false, bool, false,                                   \
   "Disassemble optimized code.")                                               \
+R(dump_megamorphic_stats, false, bool, false,                                  \
+  "Dump megamorphic cache statistics")                                         \
 R(dump_symbol_stats, false, bool, false,                                       \
   "Dump symbol table statistics")                                              \
 R(enable_asserts, false, bool, false,                                          \
   "Enable assert statements.")                                                 \
 C(enable_mirrors, false, false, bool, true,                                    \
   "Disable to make importing dart:mirrors an error.")                          \
 R(enable_type_checks, false, bool, false,                                      \
   "Enable type checks.")                                                       \
 R(error_on_bad_override, false, bool, false,                                   \
   "Report error for bad overrides.")                                           \
@@ skipping 117 matching lines @@
 P(verbose_gc_hdr, int, 40,                                                     \
   "Print verbose GC header interval.")                                         \
 R(verify_after_gc, false, bool, false,                                         \
   "Enables heap verification after GC.")                                       \
 R(verify_before_gc, false, bool, false,                                        \
   "Enables heap verification before GC.")                                      \
 D(verify_on_transition, bool, false,                                           \
   "Verify on dart <==> VM.")                                                   \
 
 #endif  // VM_FLAG_LIST_H_