Port java.util.Comparator{,s} from OpenJDK8

Also adds tests for java.util.Comparator API.

Source files are taken from jdk8u60.

Bug: 27427010
Change-Id: Id71eb7fa92c28720c13da8fd0f5f193151b6a43d
diff --git a/openjdk_java_files.mk b/openjdk_java_files.mk
index fc69ca4..fd0eebf 100644
--- a/openjdk_java_files.mk
+++ b/openjdk_java_files.mk
@@ -655,6 +655,7 @@
     ojluni/src/main/java/java/util/Collections.java \
     ojluni/src/main/java/java/util/ComparableTimSort.java \
     ojluni/src/main/java/java/util/Comparator.java \
+    ojluni/src/main/java/java/util/Comparators.java \
     ojluni/src/main/java/java/util/ConcurrentModificationException.java \
     ojluni/src/main/java/java/util/Currency.java \
     ojluni/src/main/java/java/util/Date.java \
@@ -1472,3 +1473,4 @@
     ojluni/src/lambda/java/java/lang/invoke/MethodHandleInfo.java \
     ojluni/src/lambda/java/java/lang/invoke/MethodHandles.java \
     ojluni/src/lambda/java/java/lang/invoke/MethodType.java \
+    ojluni/src/lambda/java/java/lang/invoke/SerializedLambda.java