Backport Java 11 CharSequence.compare

Test: tools/test.py --runtimes=all --no-internal -v *Backport*Test*
Test: tools/test.py --no-internal -v *GenerateBackportMethods*
Change-Id: I4e0e46d2fe1fc12ee6843a369094259472afd7f1
diff --git a/src/test/examplesJava11/backport/CharSequenceBackportJava11Main.java b/src/test/examplesJava11/backport/CharSequenceBackportJava11Main.java
new file mode 100644
index 0000000..d0888f8
--- /dev/null
+++ b/src/test/examplesJava11/backport/CharSequenceBackportJava11Main.java
@@ -0,0 +1,46 @@
+package backport;
+
+public final class CharSequenceBackportJava11Main {
+  public static void main(String[] args) {
+    testCompare();
+  }
+
+  private static void testCompare() {
+    assertTrue(CharSequence.compare("Hello", "Hello") == 0);
+
+    assertTrue(CharSequence.compare("Hey", "Hello") > 0);
+    assertTrue(CharSequence.compare("Hello", "Hey") < 0);
+
+    assertTrue(CharSequence.compare("Hel", "Hello") < 0);
+    assertTrue(CharSequence.compare("Hello", "Hel") > 0);
+
+    assertTrue(CharSequence.compare("", "") == 0);
+    assertTrue(CharSequence.compare("", "Hello") < 0);
+    assertTrue(CharSequence.compare("Hello", "") > 0);
+
+    // Different CharSequence types:
+    assertTrue(CharSequence.compare("Hello", new StringBuilder("Hello")) == 0);
+    assertTrue(CharSequence.compare(new StringBuffer("hey"), "Hello") > 0);
+    assertTrue(CharSequence.compare(new StringBuffer("Hello"), new StringBuilder("Hey")) < 0);
+
+    try {
+      throw new AssertionError(CharSequence.compare(null, "Hello"));
+    } catch (NullPointerException expected) {
+    }
+    try {
+      throw new AssertionError(CharSequence.compare("Hello", null));
+    } catch (NullPointerException expected) {
+    }
+    try {
+      // Ensure a == b fast path does not happen before null checks.
+      throw new AssertionError(CharSequence.compare(null, null));
+    } catch (NullPointerException expected) {
+    }
+  }
+
+  private static void assertTrue(boolean value) {
+    if (!value) {
+      throw new AssertionError("Expected <true> but was <false>");
+    }
+  }
+}