Add robohornet as an animation test

tools/perf/page_sets/tough_scrolling_cases.json

Index: tools/perf/page_sets/tough_scrolling_cases.json
diff --git a/tools/perf/page_sets/tough_scrolling_cases.json b/tools/perf/page_sets/tough_scrolling_cases.json
index 6487823055fa3cf996b9bf63b4253d93cd18a534..70c5f4b9c752c812daedabdb06e3d8a577fa9163 100644
--- a/tools/perf/page_sets/tough_scrolling_cases.json
+++ b/tools/perf/page_sets/tough_scrolling_cases.json
@@ -3,55 +3,55 @@
   "pages": [
     {
       "url": "file:///tough_scrolling_cases/background_fixed.html",
-      "scrolling": {
+      "smoothness": {
           "action": "scrolling_interaction"
       }
     },
     {
       "url": "file:///tough_scrolling_cases/cust_scrollbar.html",
-      "scrolling": {
+      "smoothness": {
           "action": "scrolling_interaction"
       }
     },
     {
       "url": "file:///tough_scrolling_cases/div_scrolls.html",
-      "scrolling": {
+      "smoothness": {
           "action": "scrolling_interaction"
       }
     },
     {
       "url": "file:///tough_scrolling_cases/fixed_nonstacking.html",
-      "scrolling": {
+      "smoothness": {
           "action": "scrolling_interaction"
       }
     },
     {
       "url": "file:///tough_scrolling_cases/fixed_stacking.html",
-      "scrolling": {
+      "smoothness": {
           "action": "scrolling_interaction"
       }
     },
     {
       "url": "file:///tough_scrolling_cases/iframe_scrolls.html",
-      "scrolling": {
+      "smoothness": {
           "action": "scrolling_interaction"
       }
     },
     {
       "url": "file:///tough_scrolling_cases/simple.html",
-      "scrolling": {
+      "smoothness": {
           "action": "scrolling_interaction"
       }
     },
     {
       "url": "file:///tough_scrolling_cases/wheel_body_prevdefault.html",
-      "scrolling": {
+      "smoothness": {
           "action": "scrolling_interaction"
       }
     },
     {
       "url": "file:///tough_scrolling_cases/wheel_div_prevdefault.html",
-      "scrolling": {
+      "smoothness": {
           "action": "scrolling_interaction"
       }
     }