Enable screenshot comparison in external build

This change actually enabled the screenshot comparison in the
visual regression tests. We used Docker to provision Chrome
and ChromeDriver to eliminate the discrepancy of environment
between local development and Travis CI.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=237811918

gradle/core/build.gradle

@@ -6,6 +6,15 @@ plugins {
 // used for easy inspection.
 def generatedDir = "${project.buildDir}/generated/source/custom/main"
 def resourcesDir = "${project.buildDir}/resources/main"
+def screenshotsDir = "${project.buildDir}/screenshots"
+def screenshotsForGoldensDir = "${project.buildDir}/screenshots_for_goldens"
+def newGoldensDir = "${project.buildDir}/new_golden_images"
+def goldensDir =
+  "${javatestsDir}/google/registry/webdriver/goldens/chrome-linux"
+def chromeWebdriverServicePort = 4444
+// Url to the Chrome Webdriver service used by class ChromeWebDriverPlusScreenDiffer
+def chromeWebdriverServiceUrl =
+  "http://localhost:${chromeWebdriverServicePort}/wd/hub"
 
 // Tests that conflict with (mostly unidentified) members of the main test
 // suite. It is unclear if they are offenders (i.e., those that pollute global
@@ -575,33 +584,63 @@ task outcastTest(type: Test) {
   maxParallelForks 5
 }
 
-import org.apache.tools.ant.taskdefs.condition.Os
-import java.nio.file.Files
-import java.nio.file.Paths
-ext.getChromedriver = {
-    def chromedriverZipFileName
-    if (Os.isFamily(Os.FAMILY_UNIX)) {
-        chromedriverZipFileName = 'chromedriver_linux64.zip'
-    } else if (Os.isFamily(Os.FAMILY_MAC)) {
-        chromedriverZipFileName = 'chromedriver_mac64.zip'
-    } else if (Os.isFamily(Os.FAMILY_WINDOWS)) {
-        chromedriverZipFileName = 'chromedriver_win32.zip'
-    } else {
-        throw new RuntimeException("Unsupported OS: ${OperatingSystem.getDisplayName()}")
-    }
-
-    def tempDir = Files.createTempDirectory("chromedriver-dir").toString()
-
-    ant.get(src: 'https://chromedriver.storage.googleapis.com/LATEST_RELEASE', dest: tempDir)
-    def latestReleaseVersion = Paths.get(tempDir, 'LATEST_RELEASE').readLines().get(0)
-    ant.get(src: "https://chromedriver.storage.googleapis.com/${latestReleaseVersion}/${chromedriverZipFileName}", dest: tempDir)
-    ant.unzip(src: "${tempDir}/${chromedriverZipFileName}", dest: tempDir)
-
-    def chromedriverFile = new File(tempDir, 'chromedriver')
-    chromedriverFile.setExecutable(true)
-
-    return chromedriverFile.getCanonicalPath()
+task dockerStopAtStart(type: Exec) {
+  ignoreExitValue true
+  commandLine 'docker', 'stop', 'chrome-plus-chromedriver'
 }
+task dockerStopAtEnd(type: Exec) {
+  ignoreExitValue true
+  commandLine 'docker', 'stop', 'chrome-plus-chromedriver'
+}
+
+task dockerRun(type: Exec) {
+  dependsOn dockerStopAtStart
+  def runCommand = []
+  runCommand << 'docker'
+  runCommand << 'run' << '--detach'
+  runCommand << '--name' << 'chrome-plus-chromedriver'
+  runCommand << '--publish'
+  runCommand << "${chromeWebdriverServicePort}:${chromeWebdriverServicePort}"
+  runCommand << '--volume' << '/dev/shm:/dev/shm'
+  runCommand << '--network' << 'host'
+  runCommand << '--rm'
+  runCommand << 'selenium/standalone-chrome:3.141.59-gold'
+  commandLine runCommand
+}
+
+task findGoldenImages(type: JavaExec) {
+  classpath = sourceSets.test.runtimeClasspath
+  main = 'google.registry.webdriver.GoldenImageFinder'
+
+  def arguments = []
+  arguments << "--screenshots_for_goldens_dir=${screenshotsForGoldensDir}"
+  arguments << "--new_goldens_dir=${newGoldensDir}"
+  arguments << "--existing_goldens_dir=${goldensDir}"
+  if (rootProject.findProperty("overrideExistingGoldens") == "true") {
+    arguments << "--override_existing_goldens=true"
+  }
+  args arguments
+}
+
+task generateGoldenImages(type: Test) {
+  dependsOn dockerRun
+  // Common exclude pattern. See README in parent directory for explanation.
+  exclude "**/*TestCase.*", "**/*TestSuite.*"
+  include "**/webdriver/*"
+
+  // Sets the maximum number of test executors that may exist at the same time.
+  maxParallelForks 5
+
+  systemProperty 'test.screenshot.dir', screenshotsForGoldensDir
+  systemProperty 'test.screenshot.runAllAttempts', 'true'
+  systemProperty 'test.screenshot.maxAttempts', '5'
+  systemProperty 'webdriver.chromeDriverServiceUrl', chromeWebdriverServiceUrl
+
+  doFirst {
+    new File(screenshotsForGoldensDir).deleteDir()
+  }
+}
+generateGoldenImages.finalizedBy(dockerStopAtEnd, findGoldenImages)
 
 test {
   // Common exclude pattern. See README in parent directory for explanation.
@@ -610,6 +649,8 @@ test {
   exclude outcastTestPatterns
   if (rootProject.hasProperty("excludeWebDriverTests")) {
       exclude "**/webdriver/*"
+  } else {
+      dependsOn dockerRun
   }
 
   // Run every test class in its own process.
@@ -620,11 +661,17 @@ test {
   // Sets the maximum number of test executors that may exist at the same time.
   maxParallelForks 5
 
-  // Set system property for Webdriver
-  systemProperty 'webdriver.chrome.driver', project.getChromedriver()
+  systemProperty 'webdriver.chromeDriverServiceUrl', chromeWebdriverServiceUrl
 
+  doFirst {
+    new File(screenshotsDir).deleteDir()
+  }
 }.dependsOn(fragileTest, outcastTest)
 
+if (!rootProject.hasProperty("excludeWebDriverTests")) {
+  test.finalizedBy(dockerStopAtEnd)
+}
+
 task nomulus(type: Jar) {
   manifest {
     attributes 'Main-Class': 'google.registry.tools.RegistryTool'