[asm.js] Fix infinite loop in parser on parse error.

The code in `AsmJsScanner::Next()` checks for both
end of input and parse error:

  if (token_ == kEndOfInput || token_ == kParseError) {
    return;
  }

but until now the code in the parsing loop only checked
for `kEndOfInput`, resulting in an infinite loop on
`kParseError`.

R=bradnelson@chromium.org, mstarzinger@chromium.org

Bug: chromium:771428
Change-Id: I9170f090503590b3b9b949a0d00ab4daef85bf66
Reviewed-on: https://chromium-review.googlesource.com/699994
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48290}

AUTHORS

@@ -104,6 +104,7 @@ Mike Pennisi <mike@mikepennisi.com>
 Milton Chiang <milton.chiang@mediatek.com>
 Myeong-bo Shim <m0609.shim@samsung.com>
 Nicolas Antonius Ernst Leopold Maria Kaiser <nikai@nikai.net>
+Niklas Hambüchen <mail@nh2.me>
 Noj Vek <nojvek@gmail.com>
 Oleksandr Chekhovskyi <oleksandr.chekhovskyi@gmail.com>
 Paolo Giarrusso <p.giarrusso@gmail.com>

src/asmjs/asm-parser.cc

@@ -2496,7 +2496,8 @@ void AsmJsParser::GatherCases(ZoneVector<int32_t>* cases) {
         value = static_cast<int32_t>(uvalue);
       }
       cases->push_back(value);
-    } else if (Peek(AsmJsScanner::kEndOfInput)) {
+    } else if (Peek(AsmJsScanner::kEndOfInput) ||
+               Peek(AsmJsScanner::kParseError)) {
       break;
     }
     scanner_.Next();

test/mjsunit/regress/regress-crbug-771428.js

@@ -0,0 +1,24 @@
+// Copyright 2017 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 Module() {
+  "use asm";
+  function f(i) {
+    i = i | 0;
+    switch (i | 0) {
+      case 2:
+        // Exceeds value range.
+        i = 0x1ffffffff;
+        break;
+    }
+    return i | 0;
+  }
+  return f;
+}
+var f = Module();
+assertEquals(0, f(0));
+assertEquals(1, f(1));
+assertEquals(-1, f(2));
+assertFalse(%IsAsmWasmCode(Module));