[java] Partially fixing DevTools tests by reusing the same session.

Closing the connection was a really bad idea. But detaching from the target
seriously hits performance. So let's reuse the same session as long as possible.

Unfortunately tests sometimes hand in DevTools.send with
java.util.concurrent.TimeoutException, I could not figure the pattern yet.

java/client/src/org/openqa/selenium/chromium/ChromiumDriver.java

@@ -69,6 +69,7 @@ public class ChromiumDriver extends RemoteWebDriver
   private final TouchScreen touchScreen;
   private final RemoteNetworkConnection networkConnection;
   private final Optional<Connection> connection;
+  private final Optional<DevTools> devTools;
 
   protected ChromiumDriver(CommandExecutor commandExecutor, Capabilities capabilities, String capabilityKey) {
     super(commandExecutor, capabilities);
@@ -82,6 +83,7 @@ protected ChromiumDriver(CommandExecutor commandExecutor, Capabilities capabilit
         factory,
         getCapabilities(),
         capabilityKey);
+    devTools = connection.map(DevTools::new);
   }
 
   @Override
@@ -155,8 +157,7 @@ public Map<String, Object> executeCdpCommand(String commandName, Map<String, Obj
 
   @Override
   public DevTools getDevTools() {
-    return connection.map(DevTools::new)
-        .orElseThrow(() -> new WebDriverException("Unable to create DevTools connection"));
+    return devTools.orElseThrow(() -> new WebDriverException("Unable to create DevTools connection"));
   }
 
   public String getCastSinks() {

java/client/src/org/openqa/selenium/devtools/DevTools.java

@@ -46,7 +46,8 @@ public DevTools(Connection connection) {
 
   @Override
   public void close() {
-    connection.close();
+    connection.sendAndWait(
+        cdpSession, Target.detachFromTarget(Optional.of(cdpSession), Optional.empty()), timeout);
   }
 
   public <X> X send(Command<X> command) {
@@ -61,6 +62,12 @@ public <X> void addListener(Event<X> event, Consumer<X> handler) {
     connection.addListener(event, handler);
   }
 
+  public void createSessionIfThereIsNoOne() {
+    if (cdpSession == null) {
+      createSession();
+    }
+  }
+
   public void createSession() {
     // Figure out the targets.
     List<TargetInfo> infos = connection.sendAndWait(cdpSession, Target.getTargets(), timeout);

java/client/test/org/openqa/selenium/devtools/DevToolsTestBase.java

@@ -18,10 +18,7 @@
 package org.openqa.selenium.devtools;
 
 import static org.assertj.core.api.Assumptions.assumeThat;
-import static org.openqa.selenium.testing.Safely.safelyCall;
 
-import org.assertj.core.api.Assumptions;
-import org.junit.After;
 import org.junit.Before;
 import org.openqa.selenium.testing.JUnit4TestBase;
 
@@ -35,11 +32,6 @@ public void setUp() {
     assumeThat(driver).isInstanceOf(HasDevTools.class);
 
     devTools = ((HasDevTools) driver).getDevTools();
-    devTools.createSession();
-  }
-
-  @After
-  public void tearDown() {
-    safelyCall(() -> devTools.close());
+    devTools.createSessionIfThereIsNoOne();
   }
 }