* Switch to reference delegates for garbage collection (#1410)
* Bump sequence number on resume token refresh
* Style
* Fix comment formatting
* Add FSTReferenceDelegate definition and documentation
* Add methods to return nil for delegates, wire up inMemoryPins
* Add hook for removing a reference
* Start work on reference delegates
* Fix up tests to support adding documents at a sequence number
* Implement removing references
* Remove from target when dropped from local view
* Fix warning
* Add hooks for removal from mutation queue
* Add hooks for limbo document updates
* Style
* Drop commented-out code
* Fixup after merging master
* Start importing delegate implementations
* Memory LRU tests pass
* Make memory lru work, start fixing up lru tests. All with hidden sequence numbers
* Most LRU tests passing w/ memory
* Big LRU test passes w/ memory
* Leveldb LRU tests pass
* All passing except local store tests
* All tests pass
* Fix localstore tests
* Revert removeQueryData change
* Remove collectGarbage calls
* Remove NoOp GC
* More cleanup
* Refactor FSTHelpers
* Cleanup and commenting
* Comments and cleanup
* Comments
* Drop nullable for reference delegates, and old persistence method on spec tests
* Fix missing sequence bump, remove unneeded targetID
* Style
* Drop commented-out code
* Satisfy the linters and copyrighters, etc.
* Drop more commented-out code
* Fix import -> include, NSUInteger -> int
* Start work on test comments
* FSTDocumentKey -> DocumentKey
* Sample of LRU test refactor (#1424)
* Sample of test refactor
* Drop errant 'struct' keyword
* More test refactoring
* Make gc a member variable too
* Tests refactored to use member variables
* Assign delegates procedurally, rather than passing in a block
* Fix up FSTLevelDB a little
* listens -> listenTargets
* Rename GCEnabled
* remove isSentinel
* reword comment
* Add case for non-eager GC to test
* Style
* Cleaning the lint trap
* Clean up LRU tests (#1433)
* Add copious helpers and some docs to lru tests
* Style
* Method name refactor, add comment
* Drop FSTGarbageCollector and FSTEagerGarbageCollector (#1440)
* Drop FSTGarbageCollector and FSTEagerGarbageCollector
* Drop unused containsKey from FSTLevelDBMutationQueue
* Style
* Include sequence number in FSTQueryData hash and isEqual (#1568)
* Include sequence number in FSTQueryData hash and isEqual methods
* Style
* Switch to util::Hash
* Fix preserving query cache metadata (#1569)
* Add failing test
* Move the restart tests to the leveldb test suite
* Style
* Add new persistence test helper
* Fix test failure
* Review feedback
* Style
* remove conversions in `Local` and `Remote`
* replace `FSTSnapshotVersion` in `Model`
* replace `FSTSnapshotVersion` in the rest
* let test check equal with C++ equal
* fix newly added code
* address changes
* Move all Firestore files to Objective-C++
* Update project file references
* Don't use module imports from Objective-C++
* Use extern "C" for C-accessible globals
* Work around more stringent type checking in Objective-C++
* NSMutableDictionary ivars aren't implicitly casted to NSDictionary
* FSTMaybeDocument callback can't be passed a function that accepts
FSTDocument
* NSComparisonResult can't be multiplied by -1 without casting
* Add a #include <inttypes.h> where needed
* Avoid using C++ keywords as variables
* Remove #if __cplusplus guards
Gil