port TargetIdGenerator to iOS (firebase#709)

* port TargetIdGenerator to iOS

* fix style

* move pointer property to instance variable

* TriggerTravis

Firestore/Example/Firestore.xcodeproj/project.pbxproj

@@ -111,7 +111,6 @@
 		DE51B1CE1F0D48CD0013853F /* FSTEventManagerTests.m in Sources */ = {isa = PBXBuildFile; fileRef = DE51B1AA1F0D48AC0013853F /* FSTEventManagerTests.m */; };
 		DE51B1CF1F0D48CD0013853F /* FSTQueryListenerTests.m in Sources */ = {isa = PBXBuildFile; fileRef = DE51B1AB1F0D48AC0013853F /* FSTQueryListenerTests.m */; };
 		DE51B1D01F0D48CD0013853F /* FSTQueryTests.m in Sources */ = {isa = PBXBuildFile; fileRef = DE51B1AC1F0D48AC0013853F /* FSTQueryTests.m */; };
-		DE51B1D11F0D48CD0013853F /* FSTTargetIDGeneratorTests.m in Sources */ = {isa = PBXBuildFile; fileRef = DE51B1AE1F0D48AC0013853F /* FSTTargetIDGeneratorTests.m */; };
 		DE51B1D21F0D48CD0013853F /* FSTTimestampTests.m in Sources */ = {isa = PBXBuildFile; fileRef = DE51B1AF1F0D48AC0013853F /* FSTTimestampTests.m */; };
 		DE51B1D31F0D48CD0013853F /* FSTViewSnapshotTest.m in Sources */ = {isa = PBXBuildFile; fileRef = DE51B1B01F0D48AC0013853F /* FSTViewSnapshotTest.m */; };
 		DE51B1D41F0D48CD0013853F /* FSTViewTests.m in Sources */ = {isa = PBXBuildFile; fileRef = DE51B1B11F0D48AC0013853F /* FSTViewTests.m */; };
@@ -331,7 +330,6 @@
 		DE51B1AB1F0D48AC0013853F /* FSTQueryListenerTests.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = FSTQueryListenerTests.m; sourceTree = "<group>"; };
 		DE51B1AC1F0D48AC0013853F /* FSTQueryTests.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = FSTQueryTests.m; sourceTree = "<group>"; };
 		DE51B1AD1F0D48AC0013853F /* FSTSyncEngine+Testing.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = "FSTSyncEngine+Testing.h"; sourceTree = "<group>"; };
-		DE51B1AE1F0D48AC0013853F /* FSTTargetIDGeneratorTests.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = FSTTargetIDGeneratorTests.m; sourceTree = "<group>"; };
 		DE51B1AF1F0D48AC0013853F /* FSTTimestampTests.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = FSTTimestampTests.m; sourceTree = "<group>"; };
 		DE51B1B01F0D48AC0013853F /* FSTViewSnapshotTest.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = FSTViewSnapshotTest.m; sourceTree = "<group>"; };
 		DE51B1B11F0D48AC0013853F /* FSTViewTests.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = FSTViewTests.m; sourceTree = "<group>"; };
@@ -718,7 +716,6 @@
 				DE51B1AA1F0D48AC0013853F /* FSTEventManagerTests.m */,
 				DE51B1AB1F0D48AC0013853F /* FSTQueryListenerTests.m */,
 				DE51B1AC1F0D48AC0013853F /* FSTQueryTests.m */,
-				DE51B1AE1F0D48AC0013853F /* FSTTargetIDGeneratorTests.m */,
 				DE51B1AF1F0D48AC0013853F /* FSTTimestampTests.m */,
 				DE51B1B01F0D48AC0013853F /* FSTViewSnapshotTest.m */,
 				DE51B1B11F0D48AC0013853F /* FSTViewTests.m */,
@@ -1253,7 +1250,6 @@
 				DE51B1F41F0D491B0013853F /* FSTRemoteEventTests.m in Sources */,
 				548DB927200D590300E00ABC /* assert_test.cc in Sources */,
 				54E928241F33953300C1953E /* FSTEventAccumulator.m in Sources */,
-				DE51B1D11F0D48CD0013853F /* FSTTargetIDGeneratorTests.m in Sources */,
 				5436F32420008FAD006E51E3 /* string_printf_test.cc in Sources */,
 				DE51B1EF1F0D49140013853F /* FSTDocumentTests.m in Sources */,
 				DE51B1DC1F0D490D0013853F /* FSTLocalSerializerTests.m in Sources */,

Firestore/Source/Core/FSTSyncEngine.m → Firestore/Source/Core/FSTSyncEngine.mm

@@ -22,7 +22,6 @@
 #import "Firestore/Source/Auth/FSTUser.h"
 #import "Firestore/Source/Core/FSTQuery.h"
 #import "Firestore/Source/Core/FSTSnapshotVersion.h"
-#import "Firestore/Source/Core/FSTTargetIDGenerator.h"
 #import "Firestore/Source/Core/FSTTransaction.h"
 #import "Firestore/Source/Core/FSTView.h"
 #import "Firestore/Source/Core/FSTViewSnapshot.h"
@@ -41,6 +40,8 @@
 #import "Firestore/Source/Util/FSTDispatchQueue.h"
 #import "Firestore/Source/Util/FSTLogger.h"
 
+#include "Firestore/core/src/firebase/firestore/core/target_id_generator.h"
+
 NS_ASSUME_NONNULL_BEGIN
 
 // Limbo documents don't use persistence, and are eagerly GC'd. So, listens for them don't need
@@ -141,14 +142,14 @@ @interface FSTSyncEngine ()
     NSMutableDictionary<FSTUser *, NSMutableDictionary<NSNumber *, FSTVoidErrorBlock> *>
         *mutationCompletionBlocks;
 
-/** Used for creating the FSTTargetIDs for the listens used to resolve limbo documents. */
-@property(nonatomic, strong, readonly) FSTTargetIDGenerator *targetIdGenerator;
-
 @property(nonatomic, strong) FSTUser *currentUser;
 
 @end
 
-@implementation FSTSyncEngine
+@implementation FSTSyncEngine {
+  /** Used for creating the FSTTargetIDs for the listens used to resolve limbo documents. */
+  firebase::firestore::core::TargetIdGenerator _targetIdGenerator;
+}
 
 - (instancetype)initWithLocalStore:(FSTLocalStore *)localStore
                        remoteStore:(FSTRemoteStore *)remoteStore
@@ -167,7 +168,8 @@ - (instancetype)initWithLocalStore:(FSTLocalStore *)localStore
     [_limboCollector addGarbageSource:_limboDocumentRefs];
 
     _mutationCompletionBlocks = [NSMutableDictionary dictionary];
-    _targetIdGenerator = [FSTTargetIDGenerator generatorForSyncEngineStartingAfterID:0];
+    _targetIdGenerator =
+        firebase::firestore::core::TargetIdGenerator::SyncEngineTargetIdGenerator(0);
     _currentUser = initialUser;
   }
   return self;
@@ -490,7 +492,7 @@ - (void)trackLimboChange:(FSTLimboDocumentChange *)limboChange {
 
   if (!self.limboTargetsByKey[key]) {
     FSTLog(@"New document in limbo: %@", key);
-    FSTTargetID limboTargetID = [self.targetIdGenerator nextID];
+    FSTTargetID limboTargetID = _targetIdGenerator.NextId();
     FSTQuery *query = [FSTQuery queryWithPath:key.path];
     FSTQueryData *queryData = [[FSTQueryData alloc] initWithQuery:query
                                                          targetID:limboTargetID