Accommodate Kotlin's different visibility rules.

core/src/main/java/com/google/common/truth/DoubleSubject.java

@@ -82,7 +82,7 @@ static TolerantDoubleComparison comparing(DoubleComparer comparer) {
     }
   }
 
-  private interface DoubleComparer {
+  interface DoubleComparer {
     void compareAgainst(double other);
   }
 

core/src/main/java/com/google/common/truth/FloatSubject.java

@@ -84,7 +84,7 @@ static TolerantFloatComparison comparing(FloatComparer comparer) {
     }
   }
 
-  private interface FloatComparer {
+  interface FloatComparer {
     void compareAgainst(float other);
   }
 

core/src/main/java/com/google/common/truth/IntegerSubject.java

@@ -85,7 +85,7 @@ static TolerantIntegerComparison comparing(IntegerComparer comparer) {
     }
   }
 
-  private interface IntegerComparer {
+  interface IntegerComparer {
     void compareAgainst(int other);
   }
 

core/src/main/java/com/google/common/truth/LongSubject.java

@@ -85,7 +85,7 @@ static TolerantLongComparison comparing(LongComparer comparer) {
     }
   }
 
-  private interface LongComparer {
+  interface LongComparer {
     void compareAgainst(long other);
   }
 

core/src/main/java/com/google/common/truth/SubjectUtils.java

@@ -149,7 +149,7 @@ static DuplicateGroupedAndTyped countDuplicatesAndMaybeAddTypeInfoReturnObject(
     }
   }
 
-  private static final class NonHashingMultiset<E extends @Nullable Object> {
+  static final class NonHashingMultiset<E extends @Nullable Object> {
     private final Multiset<Wrapper<E>> contents = LinkedHashMultiset.create();
 
     private NonHashingMultiset() {}