added a convenience method.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@36212 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/model/Run.java

@@ -689,7 +689,18 @@ public abstract class Run <JobT extends Job<JobT,RunT>,RunT extends Run<JobT,Run
             r=r.previousBuild;
         return r;
     }
-    
+
+    /**
+     * Returns the last successful build before this build.
+     * @since 1.383
+     */
+    public RunT getPreviousSuccessfulBuild() {
+        RunT r=previousBuild;
+        while( r!=null && r.getResult()!=Result.SUCCESS )
+            r=r.previousBuild;
+        return r;
+    }
+
     /**
      * Returns the last 'numberOfBuilds' builds with a build result >= 'threshold'.
      *