Event based project view focusing (#263)

## Problem
Previously once project import starts, the code will check periodically whether the project is ready in order to zoom into the import directory, causing GUI to be sluggish every second before project is finally loaded.

## Solution
I have found the right event to subscribe, so zooming will only happen after the project is loaded. 

## Other change
Enable test on zooming.
Clarify code on variable meaning.

src/com/twitter/intellij/pants/service/project/PantsSystemProjectResolver.java

@@ -3,6 +3,7 @@
 
 package com.twitter.intellij.pants.service.project;
 
+import com.intellij.ProjectTopics;
 import com.intellij.execution.process.ProcessAdapter;
 import com.intellij.execution.process.ProcessEvent;
 import com.intellij.execution.process.ProcessOutputTypes;
@@ -27,13 +28,17 @@
 import com.intellij.openapi.module.ModuleManager;
 import com.intellij.openapi.module.ModuleTypeId;
 import com.intellij.openapi.project.Project;
+import com.intellij.openapi.roots.ModuleRootAdapter;
+import com.intellij.openapi.roots.ModuleRootEvent;
 import com.intellij.openapi.util.Key;
 import com.intellij.openapi.util.io.FileUtil;
 import com.intellij.openapi.vfs.VirtualFile;
 import com.intellij.openapi.vfs.VirtualFileManager;
 import com.intellij.openapi.wm.ToolWindow;
+import com.intellij.openapi.wm.ToolWindowId;
 import com.intellij.openapi.wm.ToolWindowManager;
 import com.intellij.util.Consumer;
+import com.intellij.util.messages.MessageBusConnection;
 import com.twitter.intellij.pants.metrics.PantsExternalMetricsListenerManager;
 import com.twitter.intellij.pants.projectview.PantsProjectPaneSelectInTarget;
 import com.twitter.intellij.pants.projectview.ProjectFilesViewPane;
@@ -91,7 +96,18 @@ private void doViewSwitch(@NotNull ExternalSystemTaskId id, @NotNull String proj
     if (ModuleManager.getInstance(ideProject).getModules().length > 0) {
       return;
     }
-    new ViewSwitchProcessor(ideProject, projectPath).asyncViewSwitch();
+
+    MessageBusConnection messageBusConnection = ideProject.getMessageBus().connect();
+    messageBusConnection.subscribe(
+      ProjectTopics.PROJECT_ROOTS,
+      new ModuleRootAdapter() {
+        @Override
+        public void rootsChanged(ModuleRootEvent event) {
+          // Initiate view switch only when project modules have been created.
+          new ViewSwitchProcessor(ideProject, projectPath).asyncViewSwitch();
+        }
+      }
+    );
   }
 
   /**
@@ -226,10 +242,7 @@ public void asyncViewSwitch() {
       /**
        * Make sure the project view opened so the view switch will follow.
        */
-      if (ApplicationManager.getApplication().isUnitTestMode()) {
-        return;
-      }
-      final ToolWindow projectWindow = ToolWindowManager.getInstance(myProject).getToolWindow("Project");
+      final ToolWindow projectWindow = ToolWindowManager.getInstance(myProject).getToolWindow(ToolWindowId.PROJECT_VIEW);
       if (projectWindow == null) {
         return;
       }
@@ -271,7 +284,8 @@ public void run() {
                   }
                 }
               }
-              directoryFocusHandle.cancel(false);
+              final boolean mayInterruptIfRunning = true;
+              directoryFocusHandle.cancel(mayInterruptIfRunning);
             }
           });
         }