Remove prototype checks for leaf maps in optimized code.

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 209c2ade04a077b1b340251f295bbfcbdd061e12..d6391c6cf36d8295a72df22c3294267ea17f320e 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -3424,6 +3424,13 @@ bool Map::is_observed() {
   return IsObserved::decode(bit_field3());
 }
 
+void Map::NotifyObjectLayoutChange() {
+  DeoptimizeDependentCodes(DependentCodes::kPrototypeCheckGroup);
+}
+
+bool Map::CanOmitPrototypeChecks() {
+  return !HasTransitionArray() && !is_dictionary_map();
+}
 
 void Map::AddDependentCode(DependentCodes::DependencyGroup group,
                            Handle<Code> code) {
@@ -3468,20 +3475,12 @@ void DependentCodes::clear_code_at(int i) {
 }
 
 
-void DependentCodes::ComputeGroupStartIndexes(GroupStartIndexes starts) {
-  starts[0] = 0;
-  for (int g = 1; g <= kGroupCount; g++) {
-    int count = number_of_codes(static_cast<DependencyGroup>(g - 1));
-    starts[g] = starts[g - 1] + count;
-  }
-}
-
-
 void DependentCodes::ExtendGroup(DependencyGroup group) {
-  GroupStartIndexes starts;
-  ComputeGroupStartIndexes(starts);
-  for (int g = kGroupCount - 2; g > group; g--) {
-    set_code_at(starts[g + 1], code_at(starts[g]));
+  GroupStartIndexes starts(this);
+  for (int g = kGroupCount - 1; g > group; g--) {
+    if (starts.at(g) < starts.at(g + 1)) {
+      set_code_at(starts.at(g + 1), code_at(starts.at(g)));
+    }
   }
 }