Fix BlazeProjectSystemBuildManager$BuildCallbackPublisher construct…

…or signature

Nested classes registered as extensions are supposed to be static.

(cherry picked from commit fc1183f)

aswb/src/com/google/idea/blaze/android/projectsystem/BlazeProjectSystemBuildManager.java

@@ -102,7 +102,7 @@ public static BlazeBuildCounter getInstance(Project project) {
    * Class to publish BlazeBuildListener callbacks to {@link
    * BlazeProjectSystemBuildManager#PROJECT_SYSTEM_BUILD_TOPIC}
    */
-  final class BuildCallbackPublisher implements BlazeBuildListener {
+  static final class BuildCallbackPublisher implements BlazeBuildListener {
     @Override
     public void buildStarting(Project project) {
       BlazeBuildCounter.getInstance(project).onBuildStarted();