Add angle config to nanobench and make angle a default config for dm and nanobench.

NOTREECHECKS=true
R=mtklein@google.com

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/441333003
diff --git a/tools/flags/SkCommonFlags.cpp b/tools/flags/SkCommonFlags.cpp
index beeb6ee..ca2e18c 100644
--- a/tools/flags/SkCommonFlags.cpp
+++ b/tools/flags/SkCommonFlags.cpp
@@ -8,7 +8,7 @@
 #include "SkCommonFlags.h"
 #include "SkThreadPool.h"
 
-DEFINE_string(config, "565 8888 pdf gpu nonrendering",
+DEFINE_string(config, "565 8888 pdf gpu nonrendering angle",
               "Options: 565 8888 pdf gpu nonrendering msaa4 msaa16 nvprmsaa4 nvprmsaa16 "
               "gpunull gpudebug angle mesa");