[TurboFan] Fix typing of INTERNALIZED_STRING_TYPE for new EmptyString type.

Add kInternalizedNonEmptySeqString and make kInternalizedString = 
kEmptyString | kInternalizedNonEmptySeqString.

BUG=chromium:731495

Change-Id: I60a6f37242423407ad97188b3f4bd48ae6989ad2
Reviewed-on: https://chromium-review.googlesource.com/528275Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45821}

src/compiler/types.h

@@ -115,8 +115,8 @@ namespace compiler {
   V(NaN,                           1u << 11)  \
   V(Symbol,                        1u << 12)  \
   V(EmptyString,                   1u << 13)  \
-  V(InternalizedNonSeqString, 1u << 14)  \
-  V(InternalizedSeqString,    1u << 15)  \
+  V(InternalizedNonEmptySeqString, 1u << 14)  \
+  V(InternalizedNonSeqString,      1u << 15)  \
   V(OtherNonSeqString,             1u << 16)  \
   V(OtherSeqString,                1u << 17)  \
   V(OtherCallable,                 1u << 18)  \
@@ -149,16 +149,16 @@ namespace compiler {
   V(OrderedNumber,                kPlainNumber | kMinusZero) \
   V(MinusZeroOrNaN,               kMinusZero | kNaN) \
   V(Number,                       kOrderedNumber | kNaN) \
-  V(NonEmptyInternalizedString,   kInternalizedNonSeqString | \
-                                  kInternalizedSeqString) \
-  V(InternalizedString,           kNonEmptyInternalizedString | \
-                                  kEmptyString) \
+  V(InternalizedSeqString,        kEmptyString | \
+                                  kInternalizedNonEmptySeqString) \
+  V(InternalizedString,           kInternalizedSeqString | \
+                                  kInternalizedNonSeqString) \
   V(OtherString,                  kOtherNonSeqString | kOtherSeqString) \
-  V(NonEmptySeqString,            kInternalizedSeqString | kOtherSeqString) \
-  V(SeqString,                    kNonEmptySeqString | kEmptyString) \
+  V(SeqString,                    kInternalizedSeqString | kOtherSeqString) \
   V(NonSeqString,                 kInternalizedNonSeqString | \
                                   kOtherNonSeqString) \
-  V(NonEmptyString,               kNonEmptyInternalizedString | kOtherString) \
+  V(NonEmptyString,               kInternalizedNonEmptySeqString | \
+                                  kInternalizedNonSeqString| kOtherString) \
   V(String,                       kNonEmptyString | kEmptyString) \
   V(UniqueName,                   kSymbol | kInternalizedString) \
   V(Name,                         kSymbol | kString) \

test/mjsunit/compiler/regress-731495.js

+// Copyright 2016 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.
+
+// Flags: --allow-natives-syntax
+
+function foo() {
+  global = "";
+  global = global + "bar";
+  return global;
+};
+
+assertEquals(foo(), "bar");
+%OptimizeFunctionOnNextCall(foo);
+assertEquals(foo(), "bar");