[WIP] Add support for Preconditions.checkArgument(...)

[lazaroclapp]

See #47 for discussion, work in progress.

[coveralls]

Pull Request Test Coverage Report for Build #866

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 84 unchanged lines in 12 files lost coverage.
• Overall coverage increased (+0.2%) to 92.253%

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Files with Coverage Reduction	New Missed Lines	%
../nullaway/src/main/java/com/uber/nullaway/dataflow/AccessPath.java	1	96.28%
../nullaway/src/main/java/com/uber/nullaway/handlers/AssertionHandler.java	1	96.15%
../nullaway/src/main/java/com/uber/nullaway/handlers/GrpcHandler.java	1	98.21%
../nullaway/src/main/java/com/uber/nullaway/handlers/Handler.java	1	91.67%
../nullaway/src/main/java/com/uber/nullaway/handlers/Handlers.java	1	96.55%
../nullaway/src/main/java/com/uber/nullaway/handlers/RestrictiveAnnotationHandler.java	1	97.06%
../nullaway/src/main/java/com/uber/nullaway/handlers/contract/ContractHandler.java	5	91.94%
../nullaway/src/main/java/com/uber/nullaway/handlers/contract/fieldcontract/EnsuresNonNullHandler.java	6	91.55%
../nullaway/src/main/java/com/uber/nullaway/handlers/ApacheThriftIsSetHandler.java	7	83.05%
../nullaway/src/main/java/com/uber/nullaway/handlers/OptionalEmptinessHandler.java	14	83.53%

Totals
Change from base Build #865:	0.2%
Covered Lines:	4811
Relevant Lines:	5215

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💛 - Coveralls

[lazaroclapp]

Abandoning. We have a better way to do this (assuming we can get a couple visibility changes to CF APIs). Fresh PR incoming later today or tomorrow.