Initial QuadTree implementation

src/core/SkBBoxHierarchy.h

Index: src/core/SkBBoxHierarchy.h
diff --git a/src/core/SkBBoxHierarchy.h b/src/core/SkBBoxHierarchy.h
index 62b22d80e61f5ca8f64946aab6faf39e4d2e3494..0d55b71ac10259e78afdeebe190116b362a9dab1 100644
--- a/src/core/SkBBoxHierarchy.h
+++ b/src/core/SkBBoxHierarchy.h
@@ -69,6 +69,14 @@ public:
     virtual int getCount() const = 0;
 
     /**
+     * Returns the depth of the currently allocated tree.
+     * (The root node counts for 1 level, so it should be 1 or more if there's a root node)
+     * Returns 0 if there are currently no nodes in the tree.
+     * Returns -1 if the structure isn't a tree.
+     */
+    virtual int getDepth() const = 0;
+
+    /**
      * Rewinds all the most recently inserted data elements until an element
      * is encountered for which client->shouldRewind(data) returns false. May
      * not rewind elements that were inserted prior to the last call to