Don't specify heap size that exceeds the limit on 32-bit d8.
Don't specify heap size that exceeds the limit on 32-bit d8.

Currently the prebuilt d8 on ARM platform is 32-bit.

BUG=chromium:718687
TEST=page_cycler_v2 runs on ARM and x86_64 Chromebooks.

Review-Url: https://codereview.chromium.org/2872213002

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