Add property for silencing chromedriver

The Java property "webdriver.chrome.silentOutput" is now used to set the
default value for silent mode in chromedriver using the
ChromeDriverService class.

This is analogous to the existing system property for controlling
verbose mode.

Signed-off-by: Andreas Tolfsen <ato@mozilla.com>

java/client/src/org/openqa/selenium/chrome/ChromeDriverService.java

@@ -57,6 +57,13 @@ public class ChromeDriverService extends DriverService {
   public static final String CHROME_DRIVER_VERBOSE_LOG_PROPERTY =
       "webdriver.chrome.verboseLogging";
 
+  /**
+   * Boolean system property that defines whether the ChromeDriver executable should be started
+   * in silent mode.
+   */
+  public static final String CHROME_DRIVER_SILENT_OUTPUT_PROPERTY =
+      "webdriver.chrome.silentOutput";
+
   /**
    *
    * @param executable The chromedriver executable.
@@ -96,7 +103,7 @@ public static class Builder {
     String chromeLogFile = System.getProperty(CHROME_DRIVER_LOG_PROPERTY);
     private File logFile = chromeLogFile == null ? null : new File(chromeLogFile);
     private boolean verbose = Boolean.getBoolean(CHROME_DRIVER_VERBOSE_LOG_PROPERTY);
-    private boolean silent;
+    private boolean silent = Boolean.getBoolean(CHROME_DRIVER_SILENT_OUTPUT_PROPERTY);
 
     /**
      * Sets which driver executable the builder will use.