add a view for users to explore pub packages

editor/tools/plugins/com.google.dart.tools.ui/plugin.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <?eclipse version="3.4"?>
 <plugin>
 
    <extension-point id="dartElementFilters" name="%elementFiltersName" schema="schema/dartElementFilters.exsd"/>
    <extension-point id="dartEditorTextHovers" name="%javaEditorTextHoversName" schema="schema/dartEditorTextHovers.exsd"/>
    <extension-point id="dartDocCompletionProcessor" name="%javadocCompletionProcessor" schema="schema/dartDocCompletionProcessor.exsd"/>
    <extension-point id="quickFixProcessors" name="%quickFixProcessorExtensionPoint" schema="schema/quickFixProcessors.exsd"/>
    <extension-point id="quickAssistProcessors" name="%quickAssistProcessorExtensionPoint" schema="schema/quickAssistProcessors.exsd"/>
    <extension-point id="foldingStructureProviders" name="%foldingStructureProvidersExtensionPoint" schema="schema/foldingStructureProviders.exsd"/>
@@ skipping 312 matching lines @@
       </view>
 
       <view
             name="%searchViewName"
             icon="$nl$/icons/full/eview16/search_results.gif"
             category="com.google.dart.tools.ui.dart"
             class="com.google.dart.tools.search.internal.ui.SearchView"
             allowMultiple="false"
             id="com.google.dart.tools.SearchView">
       </view>
+      <view
+            category="com.google.dart.tools.ui.dart"
+            class="com.google.dart.tools.ui.internal.pub.PackagesView"
+            id="com.google.dart.tools.ui.view.packages"
+            name="Packages View"
+            restorable="true">
+      </view>
       
       <!-- view
             category="com.google.dart.tools.ui.dart"
             class="com.google.dart.tools.ui.internal.testing.DartUnitView"
             icon="icons/full/tests/testok.gif"
             id="com.google.dart.tools.ui.DartUnitView"
             name="Tests"
             restorable="true">
       </view -->
    </extension>
@@ skipping 2254 matching lines @@
         <contentTypeBinding
             contentTypeId="com.google.dart.tools.core.dartSourceFile"
             contentMergeViewerId="com.google.dart.tools.ui.internal.compare.DartContentViewerCreator">
         </contentTypeBinding>
     </extension>
     <extension
           point="org.eclipse.ui.views">
     </extension>
 
 </plugin>