[wasm] asm.js: Add asm_wasm variant to test asm.js->wasm pipeline.

tools/testrunner/local/variants.py

 # 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.
 
 # Use this to run several variants of the tests.
 ALL_VARIANT_FLAGS = {
   "default": [[]],
   "stress": [["--stress-opt", "--always-opt"]],
   "turbofan": [["--turbo"]],
   "turbofan_opt": [["--turbo", "--always-opt"]],
   "nocrankshaft": [["--nocrankshaft"]],
   "ignition": [["--ignition"]],
   "ignition_staging": [["--ignition-staging"]],
   "ignition_turbofan": [["--ignition-staging", "--turbo"]],
   "preparser": [["--min-preparse-length=0"]],
+  "asm_wasm": [["--validate-asm"]],
 }
 
 # FAST_VARIANTS implies no --always-opt.
 FAST_VARIANT_FLAGS = {
   "default": [[]],
   "stress": [["--stress-opt"]],
   "turbofan": [["--turbo"]],
   "nocrankshaft": [["--nocrankshaft"]],
   "ignition": [["--ignition"]],
   "ignition_staging": [["--ignition-staging"]],
   "ignition_turbofan": [["--ignition-staging", "--turbo"]],
   "preparser": [["--min-preparse-length=0"]],
+  "asm_wasm": [["--validate-asm"]],
 }
 
 ALL_VARIANTS = set(["default", "stress", "turbofan", "turbofan_opt",
                     "nocrankshaft", "ignition", "ignition_staging",
-                    "ignition_turbofan", "preparser"])
+                    "ignition_turbofan", "preparser", "asm_wasm"])