Bug 1033092: Add unit tests for mozilla::pkix::der::ExpectTagAndGetValue, r=keeler

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extra : rebase_source : 8ad8960969e5ee5bf47054f1c285a85cbbdb18cf
Bug 1033103: Add and use mozilla::pkix::der::ExpectTagAndGetTLV, r=keeler

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extra : rebase_source : 16461be12705998799f5c84e2043d68b0c431cb0