Change LookupForWrite to always do a full lookup and check the result.

src/arm/stub-cache-arm.cc

Index: src/arm/stub-cache-arm.cc
diff --git a/src/arm/stub-cache-arm.cc b/src/arm/stub-cache-arm.cc
index 3350c56c163762f4464dabd0e153685116b6e973..dbef0101bd0b9671f9e1a31a933d537eaed1081f 100644
--- a/src/arm/stub-cache-arm.cc
+++ b/src/arm/stub-cache-arm.cc
@@ -423,7 +423,7 @@ void StubCompiler::GenerateLoadFunctionPrototype(MacroAssembler* masm,
 // registers have their original values.
 void StubCompiler::GenerateStoreField(MacroAssembler* masm,
                                       Handle<JSObject> object,
-                                      int index,
+                                      LookupResult* lookup,
                                       Handle<Map> transition,
                                       Handle<Name> name,
                                       Register receiver_reg,
@@ -436,16 +436,6 @@ void StubCompiler::GenerateStoreField(MacroAssembler* masm,
   // r0 : value
   Label exit;
 
-  LookupResult lookup(masm->isolate());
-  object->Lookup(*name, &lookup);
-  if (lookup.IsFound() && (lookup.IsReadOnly() || !lookup.IsCacheable())) {
-    // In sloppy mode, we could just return the value and be done. However, we
-    // might be in strict mode, where we have to throw. Since we cannot tell,
-    // go into slow case unconditionally.
-    __ jmp(miss_label);
-    return;
-  }
-
   // Check that the map of the object hasn't changed.
   CompareMapMode mode = transition.is_null() ? ALLOW_ELEMENT_TRANSITION_MAPS
                                              : REQUIRE_EXACT_MAP;
@@ -460,8 +450,8 @@ void StubCompiler::GenerateStoreField(MacroAssembler* masm,
   // Check that we are allowed to write this.
   if (!transition.is_null() && object->GetPrototype()->IsJSObject()) {
     JSObject* holder;
-    if (lookup.IsFound()) {
-      holder = lookup.holder();
+    if (lookup->IsFound()) {
+      holder = lookup->holder();
     } else {
       // Find the top object.
       holder = *object;
@@ -492,6 +482,7 @@ void StubCompiler::GenerateStoreField(MacroAssembler* masm,
     return;
   }
 
+  int index;
   if (!transition.is_null()) {
     // Update the map of the object.
     __ mov(scratch1, Operand(transition));
@@ -507,6 +498,10 @@ void StubCompiler::GenerateStoreField(MacroAssembler* masm,
                         kDontSaveFPRegs,
                         OMIT_REMEMBERED_SET,
                         OMIT_SMI_CHECK);
+    index = transition->instance_descriptors()->GetFieldIndex(
+        transition->LastAdded());
+  } else {
+    index = lookup->GetFieldIndex().field_index();
   }
 
   // Adjust for the number of properties stored in the object. Even in the