Don't clear the string stub at gc time in KeyedLoadIC.

src/ic/ic.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/arguments.h"
 #include "src/base/bits.h"
@@ skipping 493 matching lines @@
       return;
     default:
       UNREACHABLE();
   }
 }
 
 
 void KeyedLoadIC::Clear(Isolate* isolate, Address address, Code* target,
                         ConstantPoolArray* constant_pool) {
   if (IsCleared(target)) return;
-  // Make sure to also clear the map used in inline fast cases.  If we
-  // do not clear these maps, cached code can keep objects alive
-  // through the embedded maps.
-  SetTargetAtAddress(address, *pre_monomorphic_stub(isolate), constant_pool);
+
+  // If the target is the string_stub, then don't clear it. It is the
+  // perfect stub if we continue to see strings. Holding this
+  // state is not preventing learning new information.
+  if (target != *isolate->builtins()->KeyedLoadIC_String()) {
+    // Make sure to also clear the map used in inline fast cases.  If we
+    // do not clear these maps, cached code can keep objects alive
+    // through the embedded maps.
+    SetTargetAtAddress(address, *pre_monomorphic_stub(isolate), constant_pool);
+  }
 }
 
 
 void CallIC::Clear(Isolate* isolate, Address address, Code* target,
                    ConstantPoolArray* constant_pool) {
   // Currently, CallIC doesn't have state changes.
 }
 
 
 void LoadIC::Clear(Isolate* isolate, Address address, Code* target,
@@ skipping 2152 matching lines @@
 static const Address IC_utilities[] = {
 #define ADDR(name) FUNCTION_ADDR(name),
     IC_UTIL_LIST(ADDR) NULL
 #undef ADDR
 };
 
 
 Address IC::AddressFromUtilityId(IC::UtilityId id) { return IC_utilities[id]; }
 }
 }  // namespace v8::internal