Add auto purging for SkPicture-related Ganesh resources (esp. layers)

tools/render_pictures_main.cpp

Index: tools/render_pictures_main.cpp
diff --git a/tools/render_pictures_main.cpp b/tools/render_pictures_main.cpp
index 13ae6ead3f22f2788cf152ef1963be7cdc02c3a2..c2c7875b282cc6cfbd8a0aa6b8a38eba0eecb678 100644
--- a/tools/render_pictures_main.cpp
+++ b/tools/render_pictures_main.cpp
@@ -205,12 +205,6 @@ static bool render_picture_internal(const SkString& inputPath, const SkString* w
         SkDebugf("Failed to render %s\n", inputFilename.c_str());
     }
 
-    if (FLAGS_preprocess) {
-        if (NULL != renderer.getCanvas()) {
-            renderer.getCanvas()->EXPERIMENTAL_purge(renderer.getPicture());
-        }
-    }
-
     renderer.end();
 
     SkDELETE(picture);