Bug 1509550 - Add more test chunks for Android 7.0 x86 jsreftests; r=me,a=test-only

taskcluster/ci/test/reftest.yml

@@ -69,7 +69,7 @@ jsreftest:
     chunks:
         by-test-platform:
             android-em-4.3-arm7-api-16/debug: 100
-            android-em-7.0-x86/opt: 3
+            android-em-7.0-x86/opt: 4
             android-em.*: 40
             windows.*: 2
             windows10-64-ccov/debug: 5