* Use bridged __weak reference instead CFRetain/CFRelease
* Use SecKeyRef instead of FIRInstanceIDKeyPair for the memory management test
* Use SecKeyGeneratePair instead of SecKeyCreateRandomKey available since iOS 10 only
* FIRInstanceIDKeyPairStoreTest wait until all keychain operations finished before finishing a test
* FIRInstanceIDTokenManagerTest: cleanup in tearDown; fix expectation to produce an error nor a crash.
* Use properties instead of ivars FIRInstanceIDTokenManagerTest
* FIRInstanceIDTokenManager fix OCMPartialMock() usage.
Maksym Malyhin