The JettyAppServer crashes if it can't find javascript resources

on startup. This is not ideal with bazel since we're still sorting
out build rules and the data dependencies haven't been nailed down.

As a quick fix to move forward, introduce a system property to
ignore the missing JS roots:
    -Dorg.openqa.selenium.environment.webserver.ignoreMissingJsRoots=true

The server will still crash if it cannot find common/src/web, as
those dependencies are critical for the selenium test suite.

java/client/test/org/openqa/selenium/environment/webserver/JettyAppServer.java

@@ -56,6 +56,7 @@
 import org.seleniumhq.jetty9.util.ssl.SslContextFactory;
 
 import java.io.File;
+import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.net.URL;
 import java.nio.file.Files;
@@ -115,10 +116,10 @@ public JettyAppServer(String hostName, int httpPort, int httpsPort) {
     Path webSrc = locate("common/src/web");
     ServletContextHandler defaultContext = addResourceHandler(
         DEFAULT_CONTEXT_PATH, webSrc);
-    ServletContextHandler jsContext = addResourceHandler(
-        JS_SRC_CONTEXT_PATH, locate("javascript"));
-    addResourceHandler(CLOSURE_CONTEXT_PATH, locate("third_party/closure/goog"));
-    addResourceHandler(THIRD_PARTY_JS_CONTEXT_PATH, locate("third_party/js"));
+
+    addJsResourceHandler(JS_SRC_CONTEXT_PATH, "javascript");
+    addJsResourceHandler(CLOSURE_CONTEXT_PATH, "third_party/closure/goog");
+    addJsResourceHandler(THIRD_PARTY_JS_CONTEXT_PATH, "third_party/js");
 
     TemporaryFilesystem tempFs = TemporaryFilesystem.getDefaultTmpFS();
     tempPageDir = tempFs.createTempDir("pages", "test");
@@ -148,6 +149,22 @@ public JettyAppServer(String hostName, int httpPort, int httpsPort) {
     addServlet(defaultContext, "/createPage", CreatePageServlet.class);
   }
 
+  private void addJsResourceHandler(String handlerPath, String dirPath) {
+    Path path;
+    try {
+      path = locate(dirPath);
+    } catch (WebDriverException e) {
+      // Ugly hack to get us started with bazel while sorting out missing data dependencies.
+      if (Boolean.getBoolean(getClass().getPackage().getName() + ".ignoreMissingJsRoots")
+          && e.getCause() instanceof FileNotFoundException) {
+        System.err.println("WARNING: failed to add resource handler " + handlerPath + ": " + e.getCause());
+        return;
+      }
+      throw e;
+    }
+    addResourceHandler(handlerPath, path);
+  }
+
   private static Optional<Integer> getEnvValue(String key) {
     return Optional.ofNullable(System.getenv(key)).map(Integer::parseInt);
   }