Wait for UI plugins to load

If a screen is registered by a plugin this registration needs to be
completed before the dispatcher tries to parse the token.  Wait for
plugin scripts to finish loading and evaluating.  The old method of
injecting a script tag was not waiting correctly, especially for GWT
based plugins.

JavaScript plugins are now required to use Gerrit.install() as this
method updates internal Gerrit state tracking the script.  Not using
install() will eventually cause the UI to report the plugin as failing
to load.

GWT plugins must override onPluginLoad() not onModuleLoad().  All
plugins must recompile with the new glue code, as there is now a
handshake between the GWT plugin and the main Gerrit code.

All plugins must load within 5 seconds, otherwise the page marks them
as failed and reports loading errors.  During loading a glass pane is
used to prevent the user from interacting with a partial initialized
UI.  Plugins may be making critical contributions that need to be
registered before use.

A chunk of the API glue code was moved around to make each JSNI block
smaller, and better isolate purpose.  Plugin is now declared in its
own Java class.

Plugin instances are now tracked in the map $wnd.Gerrit.plugins.
This allows the main code to later figure out if any instance failed
to load. Any loading errors are usually reported on the JavaScript
console as script failures, and may include stack traces.

Change-Id: Id03581437ae1010cf995ef7ba8626ece37dfc2f4

gerrit-gwtui/src/main/java/com/google/gerrit/client/Gerrit.java

@@ -22,6 +22,7 @@ import com.google.gerrit.client.account.AccountCapabilities;
 import com.google.gerrit.client.account.AccountInfo;
 import com.google.gerrit.client.admin.ProjectScreen;
 import com.google.gerrit.client.api.ApiGlue;
+import com.google.gerrit.client.api.PluginLoader;
 import com.google.gerrit.client.changes.ChangeConstants;
 import com.google.gerrit.client.changes.ChangeListScreen;
 import com.google.gerrit.client.config.ConfigServerApi;
@@ -49,12 +50,8 @@ import com.google.gerrit.reviewdb.client.AccountGeneralPreferences;
 import com.google.gerrit.reviewdb.client.AuthType;
 import com.google.gerrit.reviewdb.client.Project;
 import com.google.gwt.aria.client.Roles;
-import com.google.gwt.core.client.Callback;
-import com.google.gwt.core.client.CodeDownloadException;
 import com.google.gwt.core.client.EntryPoint;
 import com.google.gwt.core.client.GWT;
-import com.google.gwt.core.client.JavaScriptObject;
-import com.google.gwt.core.client.ScriptInjector;
 import com.google.gwt.dom.client.AnchorElement;
 import com.google.gwt.dom.client.Document;
 import com.google.gwt.event.dom.client.ClickEvent;
@@ -84,12 +81,9 @@ import com.google.gwt.user.client.ui.RootPanel;
 import com.google.gwtexpui.clippy.client.CopyableLabel;
 import com.google.gwtexpui.user.client.UserAgent;
 import com.google.gwtexpui.user.client.ViewSite;
-import com.google.gwtjsonrpc.client.CallbackHandle;
 import com.google.gwtjsonrpc.client.JsonDefTarget;
 import com.google.gwtjsonrpc.client.JsonUtil;
 import com.google.gwtjsonrpc.client.XsrfManager;
-import com.google.gwtjsonrpc.client.impl.ResultDeserializer;
-import com.google.gwtjsonrpc.common.AsyncCallback;
 import com.google.gwtorm.client.KeyUtil;
 
 import java.util.HashMap;
@@ -571,7 +565,7 @@ public class Gerrit implements EntryPoint {
     }
 
     saveDefaultTheme();
-    loadPlugins(hpd, token);
+    PluginLoader.load(hpd.plugins, token);
   }
 
   private void saveDefaultTheme() {
@@ -580,53 +574,6 @@ public class Gerrit implements EntryPoint {
         Document.get().getElementById("gerrit_footer"));
   }
 
-  private void loadPlugins(HostPageData hpd, final String token) {
-    if (hpd.plugins != null && !hpd.plugins.isEmpty()) {
-      for (final String url : hpd.plugins) {
-        ScriptInjector.fromUrl(url)
-            .setWindow(ScriptInjector.TOP_WINDOW)
-            .setCallback(new Callback<Void, Exception>() {
-              @Override
-              public void onSuccess(Void result) {
-              }
-
-              @Override
-              public void onFailure(Exception reason) {
-                ErrorDialog d;
-                if (reason instanceof CodeDownloadException) {
-                  d = new ErrorDialog(M.cannotDownloadPlugin(url));
-                } else {
-                  d = new ErrorDialog(M.pluginFailed(url));
-                }
-                d.center();
-              }
-            }).inject();
-      }
-    }
-
-    CallbackHandle<Void> cb = new CallbackHandle<Void>(
-        new ResultDeserializer<Void>() {
-          @Override
-          public Void fromResult(JavaScriptObject responseObject) {
-            return null;
-          }
-        },
-        new AsyncCallback<Void>() {
-          @Override
-          public void onFailure(Throwable caught) {
-          }
-
-          @Override
-          public void onSuccess(Void result) {
-            display(token);
-          }
-        });
-    cb.install();
-    ScriptInjector.fromString(cb.getFunctionName() + "();")
-        .setWindow(ScriptInjector.TOP_WINDOW)
-        .inject();
-  }
-
   public static void refreshMenuBar() {
     menuLeft.clear();
     menuRight.clear();