Add support for plugin-owned capabilities

Plugin contributed SSH commands and UiActions can now be annotated
with plugin-owned capabilities.

Capability scope was introduced to differentiate between plugin-owned
capabilities and core capabilities. Per default the scope of
@RequiresCapability annotation is CapabilityScope.CONTEXT, i. e. when
@RequiresCapability is used within a plugin the scope of the capability is
assumed to be that plugin. If @RequiresCapability is used within the core
Gerrit Code Review server (and thus is outside of a plugin) the scope is the
core server and will use the GlobalCapability known to Gerrit Code Review
server.

If a plugin needs to use a core capability name (e.g. "administrateServer")
this can be specified by setting scope = CapabilityScope.CORE:

  @RequiresCapability(value="administrateServer", scope=CapabilityScope.CORE)

Change-Id: I82f7a6fef2a47613a1fd9c7474ff568db3ca84a2

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/annotations/CapabilityScope.java

@@ -0,0 +1,36 @@
+// Copyright (C) 2013 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.extensions.annotations;
+
+/** Declared scope of a capability named by {@link RequiresCapability}. */
+public enum CapabilityScope {
+  /**
+   * Scope is assumed based on the context.
+   *
+   * When {@code @RequiresCapability} is used within a plugin the scope of the
+   * capability is assumed to be that plugin.
+   *
+   * If {@code @RequiresCapability} is used within the core Gerrit Code Review
+   * server (and thus is outside of a plugin) the scope is the core server and
+   * will use {@link com.google.gerrit.common.data.GlobalCapability}.
+   */
+  CONTEXT,
+
+  /** Scope is only the plugin. */
+  PLUGIN,
+
+  /** Scope is the core server. */
+  CORE;
+}

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/annotations/RequiresCapability.java

@@ -27,5 +27,9 @@ import java.lang.annotation.Target;
 @Target({ElementType.TYPE})
 @Retention(RUNTIME)
 public @interface RequiresCapability {
+  /**  Name of the capability required to invoke this action. */
   String value();
+
+  /** Scope of the named capability. */
+  CapabilityScope scope() default CapabilityScope.CONTEXT;
 }