[test] Bump timeout for js-test Strings on Android

The test still runs into the 240s timeout on Nexus5 and
Nexus7.

NOTRY=true
TBR=adamk, caitp

Review-Url: https://codereview.chromium.org/2406173002
Cr-Commit-Position: refs/heads/master@{#40151}

test/js-perf-test/JSTests.json

@@ -119,6 +119,7 @@
       "results_regexp": "^%s\\-Strings\\(Score\\): (.+)$",
       "run_count": 1,
       "timeout": 240,
+      "timeout_android_arm": 360,
       "tests": [
         {"name": "StringFunctions"}
       ]