Service lookup should use interface (#757)

* Resolve service using interface and initialize just once.

The ServiceManager basically maps interface types to implementations
based off of the plugin.xml.  Make sure to retrieve the implementations
using the interface type and not the implementation type.

I'm also moving the initialization to the constructor since the client
type should never change at runtime.

* remove redundant import

* added constructor javdoc

Author: patflynn

google-account-plugin/src/com/google/cloud/tools/intellij/stats/GoogleUsageTracker.java

@@ -16,7 +16,7 @@
 
 package com.google.cloud.tools.intellij.stats;
 
-import com.google.cloud.tools.intellij.IdeaAccountPluginInfoService;
+import com.google.cloud.tools.intellij.AccountPluginInfoService;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Lists;
 
@@ -51,9 +51,16 @@ public class GoogleUsageTracker implements UsageTracker {
   private static final String ANALYTICS_URL = "https://ssl.google-analytics.com/collect";
 
   private final String analyticsId;
+  private String externalPluginName;
 
+  /**
+   * Constructs a usage tracker configured with analytics and plugin name configured from its
+   * environment.
+   */
   public GoogleUsageTracker() {
-    this.analyticsId = UsageTrackerManager.getInstance().getAnalyticsProperty();
+    analyticsId = UsageTrackerManager.getInstance().getAnalyticsProperty();
+    externalPluginName = ServiceManager.getService(AccountPluginInfoService.class)
+        .getExternalPluginName();
   }
 
   private static final List<BasicNameValuePair> analyticsBaseData = ImmutableList
@@ -80,9 +87,6 @@ public void trackEvent(@NotNull String eventCategory,
 
         List<BasicNameValuePair> postData = Lists.newArrayList(analyticsBaseData);
         postData.add(new BasicNameValuePair("tid", analyticsId));
-
-        String externalPluginName =
-            ServiceManager.getService(IdeaAccountPluginInfoService.class).getExternalPluginName();
         postData.add(new BasicNameValuePair("cd19", externalPluginName));  // Event type
         postData.add(new BasicNameValuePair("cd20", eventAction));  // Event name
         postData.add(new BasicNameValuePair("cd16", "0"));  // Internal user? No.