Bug 857382 (part 1) - Correctly handle memory report files that have no measurements in the "explicit" or "other" sections.  r=kats.

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extra : rebase_source : 2fa86e1a5b0729f2deee3f1f15989685fb2e5d77
Bug 857382 (part 2) - Prefix zone addresses in about:memory with "0x" for consistenty with other addresses.  r=billm.

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extra : rebase_source : a8c669c0bf27fa0b1d90c9b7862ca43dfe4a80bd
Bug 857382 (part 3) - Add ability to diff two files to about:memory.  r=kats.

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extra : rebase_source : d5cfd7a690b1de7ce0b18ef45fbb03fc6cb9fc23