Bug 1057222 - Do partial tile uploads on desktop. r=BenWa

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extra : rebase_source : 47ef135eeb5a2f1c9b97594fa7bc7bcd90360cd2
Bug 1057222 - Avoid uploading the whole tile when it's new but only partially valid. r=BenWa

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extra : rebase_source : 8fe73f903f2917830f05fd82a865a5376ecab31c