[wasm][asm.js] Permit ternary operator in asm.js returns in some cases.

test/cctest/asmjs/test-asm-typer.cc

 // 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.
 
 #include <cstring>
 #include <functional>
 #include <iostream>
 #include <memory>
 
 #include "src/asmjs/asm-typer.h"
@@ skipping 838 matching lines @@
       {"function f(a) {\n"
        "  a = a|0;\n"
        "  return a;\n"
        "}\n",
        "in return statement is not const"},
       {"function f() {\n"
        "  return a;\n"
        "}\n",
        "Undeclared identifier in return statement"},
       {"function f() {\n"
+       "  var i = 0;\n"
        "  return i?0:1;\n"
        "}\n",
-       "Invalid return type expression"},
+       "Type mismatch in return statement"},
       {"function f() {\n"
        "  return stdlib.Math.E;"
        "}\n",
        "Invalid return type expression"},
       {"function f() {\n"
        "  return E[0];"
        "}\n",
        "Invalid return type expression"},
       {"function I() {}\n", "Identifier redefined as function"},
       {"function foo() {}\n", "Identifier redefined as function"},
@@ skipping 1205 matching lines @@
     if (!ValidationOf(Module(kTests[ii]))
              ->FailsWithMessage(
                  "Constant in return must be signed, float, or double.")) {
       std::cerr << "Test:\n" << kTests[ii];
       CHECK(false);
     }
   }
 }
 
 }  // namespace