Bug 840902. Part 1: Stop checking the results of various display list methods. r=mattwoodrow

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extra : rebase_source : b7db21120cdd96342502db64916b0b2e75c0a9c3
Bug 840902. Part 2: Remove nsresults from various display list methods. r=mattwoodrow

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extra : rebase_source : ce01b066f803e048c0e38e5316ce96a75e689418