Add Event and EventTest

remoting/android/java/src/org/chromium/chromoting/Preconditions.java

Index: remoting/android/java/src/org/chromium/chromoting/Preconditions.java
diff --git a/remoting/android/java/src/org/chromium/chromoting/Preconditions.java b/remoting/android/java/src/org/chromium/chromoting/Preconditions.java
new file mode 100644
index 0000000000000000000000000000000000000000..b91fdf29c4df721c0b18dd8b3bdbad655a4b8e0a
--- /dev/null
+++ b/remoting/android/java/src/org/chromium/chromoting/Preconditions.java
@@ -0,0 +1,33 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.chromoting;
+
+/**
+ * A set of helper functions to write assertions. These functions are always being executed, and
+ * will not ignored in release build.
+ */
+
+public final class Preconditions {
+    // This class contains only static functions, so it should not be instantiated.
+    private Preconditions() {}
+
+    // Checks whether input |v| is true, and returns its value. Throws
+    // {@link IllegalStateException} if |v| is false.
+    public static final boolean isTrue(boolean v) {
+        if (!v) {
+            throw new IllegalStateException();
+        }
+        return v;
+    }
+
+    // Checks whether input |ref| is not a null reference, and return its value. Throws
+    // {@link NullPointerException} if |ref| is null.
+    public static final <T> T notNull(T ref) {
+        if (ref == null) {
+            throw new NullPointerException();
+        }
+        return ref;
+    }
+}