Make BBoxHierarchy ref-counted, fix leak in RTreeTest.
Review URL: https://codereview.appspot.com/6489108

git-svn-id: http://skia.googlecode.com/svn/trunk@5484 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/bench/RTreeBench.cpp b/bench/RTreeBench.cpp
index edea57d..d13d887 100644
--- a/bench/RTreeBench.cpp
+++ b/bench/RTreeBench.cpp
@@ -37,7 +37,7 @@
         }
     }
     virtual ~BBoxBuildBench() {
-        delete fTree;
+        fTree->unref();
     }
 protected:
     virtual const char* onGetName() {
@@ -93,7 +93,7 @@
         fTree->flushDeferredInserts();
     }
     virtual ~BBoxQueryBench() {
-        delete fTree;
+        fTree->unref();
     }
 protected:
     virtual const char* onGetName() {