[tools] Double timeout for JSTests

R=machenbach@chromium.org

Bug: chromium:775123
Change-Id: I8ca24e48c978b754b8cf9d455ae9314d730104c3
Reviewed-on: https://chromium-review.googlesource.com/800071Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Sergiy Byelozyorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49745}

test/js-perf-test/JSTests.json

@@ -514,6 +514,7 @@
           "resources": [ "arithmetic.js" ],
           "test_flags": [ "arithmetic" ],
           "results_regexp": "^%s\\-BytecodeHandler\\(Score\\): (.+)$",
+          "timeout": 240,
           "tests": [
             {"name": "Smi-Add"},
             {"name": "Number-Add"},