Support ChromeDriver "append log" flag in Java

ChromeDriver has a command line option to append to existing log file
instead of overwriting it. Update Java API to support it.

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

@@ -46,6 +46,12 @@ public class ChromeDriverService extends DriverService {
    */
   public final static String CHROME_DRIVER_LOG_PROPERTY = "webdriver.chrome.logfile";
 
+  /**
+   * Boolean system property that defines whether chromedriver should append to existing log file.
+   */
+  public static final String CHROME_DRIVER_APPEND_LOG_PROPERTY =
+      "webdriver.chrome.appendLog";
+
   /**
    * Boolean system property that defines whether the chromedriver executable should be started
    * with verbose logging.
@@ -101,6 +107,7 @@ public static ChromeDriverService createDefaultService() {
   public static class Builder extends DriverService.Builder<
       ChromeDriverService, ChromeDriverService.Builder> {
 
+    private boolean appendLog = Boolean.getBoolean(CHROME_DRIVER_APPEND_LOG_PROPERTY);
     private boolean verbose = Boolean.getBoolean(CHROME_DRIVER_VERBOSE_LOG_PROPERTY);
     private boolean silent = Boolean.getBoolean(CHROME_DRIVER_SILENT_OUTPUT_PROPERTY);
     private String whitelistedIps = System.getProperty(CHROME_DRIVER_WHITELISTED_IPS_PROPERTY);
@@ -120,6 +127,17 @@ public int score(Capabilities capabilities) {
       return score;
     }
 
+    /**
+     * Configures the driver server appending to log file.
+     *
+     * @param verbose True for appending to log file, false otherwise.
+     * @return A self reference.
+     */
+    public Builder withAppendLog(boolean appendLog) {
+      this.appendLog = appendLog;
+      return this;
+    }
+
     /**
      * Configures the driver server verbosity.
      *
@@ -176,6 +194,9 @@ protected ImmutableList<String> createArgs() {
       if (getLogFile() != null) {
         argsBuilder.add(String.format("--log-path=%s", getLogFile().getAbsolutePath()));
       }
+      if (appendLog) {
+        argsBuilder.add("--append-log");
+      }
       if (verbose) {
         argsBuilder.add("--verbose");
       }