Introduce a PrototypeIterator template and use it all over the place

src/stub-cache.cc

Index: src/stub-cache.cc
diff --git a/src/stub-cache.cc b/src/stub-cache.cc
index c15038ee9ecc3f13c63ae159a2bea5af453c3262..9ac30d4ecec45fcae79e488482776c3a6365a63b 100644
--- a/src/stub-cache.cc
+++ b/src/stub-cache.cc
@@ -11,6 +11,7 @@
 #include "src/cpu-profiler.h"
 #include "src/gdb-jit.h"
 #include "src/ic-inl.h"
+#include "src/prototype-iterator.h"
 #include "src/stub-cache.h"
 #include "src/type-info.h"
 #include "src/vm-state-inl.h"
@@ -706,8 +707,8 @@ void StubCompiler::LookupPostInterceptor(Handle<JSObject> holder,
                                          LookupResult* lookup) {
   holder->LookupOwnRealNamedProperty(name, lookup);
   if (lookup->IsFound()) return;
-  if (holder->GetPrototype()->IsNull()) return;
-  holder->GetPrototype()->Lookup(name, lookup);
+  if (SAFE_GET_PROTOTYPE_FAST(*holder)->IsNull()) return;
+  SAFE_GET_PROTOTYPE_FAST(*holder)->Lookup(name, lookup);
 }
 
 
@@ -977,7 +978,7 @@ Handle<Code> StoreStubCompiler::CompileStoreTransition(
   __ CheckMapDeprecated(transition, scratch1(), &miss);
 
   // Check that we are allowed to write this.
-  if (object->GetPrototype()->IsJSObject()) {
+  if (SAFE_GET_PROTOTYPE_FAST(*object)->IsJSObject()) {
     Handle<JSObject> holder;
     // holder == object indicates that no property was found.
     if (lookup->holder() != *object) {
@@ -985,9 +986,12 @@ Handle<Code> StoreStubCompiler::CompileStoreTransition(
     } else {
       // Find the top object.
       holder = object;
-      do {
-        holder = Handle<JSObject>(JSObject::cast(holder->GetPrototype()));
-      } while (holder->GetPrototype()->IsJSObject());
+      for (PrototypeIterator<STORE_AS_POINTER, MAP_BASED_WALK,
+                             END_AT_NULL_VALUE> iter(*holder);
+           !iter.IsAtEnd(); iter.Advance()) {
+        SLOW_ASSERT(iter.GetCurrent()->IsJSObject());
+        holder = Handle<JSObject>(JSObject::cast(iter.GetCurrent()));
+      }
     }
 
     Register holder_reg = HandlerFrontendHeader(