Create an injectable LockHandler

We create an injectable LockHandler that just calls the static
Lock.executeWithLocks function.

I'm not sure what's the correct place to put the LockHandler. I think
model/server is only appropriate for the actual datastore lock. This is a "per request" lock, so maybe request/lock?

-----------------------------

This is the initial step in adding the "lock implicitly released on request death" feature, but it's also useful on its own - easier to test Actions when we can use a fake lock.

To keep this CL simple, we keep using the old Lock as is in most places. We just choose a single example to convert to LockHandler to showcase it. Converting all other uses will be in a subsequent CL.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=167357564

javatests/google/registry/testing/FakeLockHandler.java

@@ -0,0 +1,57 @@
+// Copyright 2017 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.testing;
+
+import static com.google.common.base.Throwables.throwIfUnchecked;
+
+import google.registry.request.lock.LockHandler;
+import java.util.concurrent.Callable;
+import javax.annotation.Nullable;
+import org.joda.time.Duration;
+
+/** A fake {@link LockHandler} where user can control if lock acquisition succeeds. */
+public class FakeLockHandler implements LockHandler {
+
+  private static final long serialVersionUID = 6437880915118738492L;
+
+  boolean lockSucceeds = true;
+
+  /**
+   * @param lockSucceeds if true - the lock acquisition will succeed and the callable will be
+   * called. If false, lock acquisition will fail and the caller isn't called.
+   */
+  public FakeLockHandler(boolean lockSucceeds) {
+    this.lockSucceeds = lockSucceeds;
+  }
+
+  @Override
+  public boolean executeWithLocks(
+      final Callable<Void> callable,
+      @Nullable String tld,
+      Duration leaseLength,
+      String... lockNames) {
+    if (!lockSucceeds) {
+      return false;
+    }
+
+    try {
+      callable.call();
+    } catch (Exception e) {
+      throwIfUnchecked(e);
+      throw new RuntimeException(e);
+    }
+    return true;
+  }
+}