Bug 986114 - Pre: introduce BaseRobocopTest, rework testBrowserProviderPerf. r=nalexander
Bug 986114 - Pre: clean up testReadingListProvider. r=trivial
Bug 986114 - Part 1: ReadingListProvider and BrowserProvider should share DB accessors. r=nalexander
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Bug 986114 - Follow-up: Fix bustage on a CLOSED TREE.
Bug 986114 - Part 2: switch TabsProvider to use PerProfileDatabaseProvider. r=nalexander