render_pdfs cull rect output formated better

Review URL: https://codereview.chromium.org/657353004
diff --git a/tools/render_pdfs_main.cpp b/tools/render_pdfs_main.cpp
index dd5f642..5e3385e 100644
--- a/tools/render_pdfs_main.cpp
+++ b/tools/render_pdfs_main.cpp
@@ -254,7 +254,7 @@
             ++failures;
             continue;
         }
-        SkDebugf("[%f,%f,%f,%f] %-*s", 
+        SkDebugf("[%6g %6g %6g %6g] %-*s",
             picture->cullRect().fLeft, picture->cullRect().fTop,
             picture->cullRect().fRight, picture->cullRect().fBottom,
             maximumPathLength, basename.c_str());