[turbofan] Support for ConsString by escape analysis.

test/mjsunit/regress/regress-crbug-648737.js

Index: test/mjsunit/regress/regress-crbug-648737.js
diff --git a/test/mjsunit/regress/regress-crbug-648737.js b/test/mjsunit/regress/regress-crbug-648737.js
new file mode 100644
index 0000000000000000000000000000000000000000..22f85515435e3a733265cd756f0720ba4790e8d1
--- /dev/null
+++ b/test/mjsunit/regress/regress-crbug-648737.js
@@ -0,0 +1,24 @@
+// 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 --turbo --turbo-escape
+
+function f(str) {
+  var s = "We turn {" + str + "} into a ConsString now";
+  return s.length;
+}
+assertEquals(33, f("a"));
+assertEquals(33, f("b"));
+%OptimizeFunctionOnNextCall(f);
+assertEquals(33, f("c"));
+
+function g(str) {
+  var s = "We also try to materalize {" + str + "} when deopting";
+  %DeoptimizeNow();
+  return s.length;
+}
+assertEquals(43, g("a"));
+assertEquals(43, g("b"));
+%OptimizeFunctionOnNextCall(g);
+assertEquals(43, g("c"));