Bug 862053 - Use getBoundingClientRect instead of offsetParents, r=mdas, a=test-only

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extra : amend_source : be769b2cbe030854585ab980edcb6ffdb36d6039
extra : transplant_source : %84%F1%BE%EC1%DA%EF%A9%05%CD%B3F%EBAX.%27%F6%87%D1