[Android] Add ApiCompatibilityUtils.requireNonNull

This CL adds ApiCompatibilityUtils.requireNonNull method that behaves
identically to Objects.requireNonNull added in API level 19 (see
https://developer.android.com/reference/java/util/Objects). This method
does what the name says - it ensures that passed object is not null.

Bug: None
Change-Id: Ia9a1b32f34569208f2eea67fc998fe1d3fca613d
Reviewed-on: https://chromium-review.googlesource.com/1097404
Commit-Queue: Boris Sazonov <bsazonov@chromium.org>
Reviewed-by: Tommy Nyquist <nyquist@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567842}

base/android/java/src/org/chromium/base/ApiCompatibilityUtils.java

@@ -31,6 +31,7 @@ import android.os.StatFs;
 import android.os.StrictMode;
 import android.os.UserManager;
 import android.provider.Settings;
+import android.support.annotation.NonNull;
 import android.text.Html;
 import android.text.Spanned;
 import android.view.View;
@@ -68,6 +69,29 @@ public class ApiCompatibilityUtils {
         return lhs == rhs ? 0 : lhs ? 1 : -1;
     }
 
+    /**
+     * Checks that the object reference is not null and throws NullPointerException if it is.
+     * See {@link Objects#requireNonNull} which is available since API level 19.
+     * @param obj The object to check
+     */
+    @NonNull
+    public static <T> T requireNonNull(T obj) {
+        if (obj == null) throw new NullPointerException();
+        return obj;
+    }
+
+    /**
+     * Checks that the object reference is not null and throws NullPointerException if it is.
+     * See {@link Objects#requireNonNull} which is available since API level 19.
+     * @param obj The object to check
+     * @param message The message to put into NullPointerException
+     */
+    @NonNull
+    public static <T> T requireNonNull(T obj, String message) {
+        if (obj == null) throw new NullPointerException(message);
+        return obj;
+    }
+
     /**
      * {@link String#getBytes()} but specifying UTF-8 as the encoding and capturing the resulting
      * UnsupportedEncodingException.