Implement screenshot comparison

This change added the implementation of screenshot comparison with
ChromeWebDriver which will be used in the open-source code base.

This change also set a default window size(1200x2000) for each screenshot
test. This is to make the size of screenshot deterministic to help
build the screenshot comparison tests.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=235539713

javatests/google/registry/webdriver/RepeatableRunner.java

@@ -0,0 +1,73 @@
+// Copyright 2019 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.webdriver;
+
+import com.google.common.flogger.FluentLogger;
+import org.junit.runners.BlockJUnit4ClassRunner;
+import org.junit.runners.model.FrameworkMethod;
+import org.junit.runners.model.InitializationError;
+import org.junit.runners.model.Statement;
+
+/**
+ * A JUnit test runner which can retry each test up to 3 times.
+ *
+ * <p>This runner is for our visual regression to prevent flakes
+ * during the run. The test is repeated multiple times until it
+ * passes and it only fails if it failed 3 times.
+ */
+public class RepeatableRunner extends BlockJUnit4ClassRunner {
+
+  private static final FluentLogger logger = FluentLogger.forEnclosingClass();
+
+  private static final int MAX_ATTEMPTS = 3;
+
+  /** Constructs a new instance of the default runner */
+  public RepeatableRunner(Class<?> klass) throws InitializationError {
+    super(klass);
+  }
+
+  @Override
+  protected Statement methodBlock(FrameworkMethod method) {
+    Statement statement = super.methodBlock(method);
+    return new RepeatableStatement(statement, method);
+  }
+
+  private static class RepeatableStatement extends Statement {
+
+    private Statement statement;
+    private FrameworkMethod method;
+
+    public RepeatableStatement(Statement statement, FrameworkMethod method) {
+      this.statement = statement;
+      this.method = method;
+    }
+
+    @Override
+    public void evaluate() throws Throwable {
+      for (int i = 1; i <= MAX_ATTEMPTS; i++) {
+        try {
+          statement.evaluate();
+          return;
+        } catch (Throwable e) {
+          logger.atSevere().log(
+              "[%s] Attempt %d of %d failed!\n", method.getName(), i, MAX_ATTEMPTS);
+          if (i == MAX_ATTEMPTS) {
+            throw e;
+          }
+        }
+      }
+    }
+  }
+}