Don't skip flaky test, but marking them as experimental

In https://chromium-review.googlesource.com/c/chromium/src/+/2391502 two
tests were marked to be skipped as they were flaky.

According to https://chromium.googlesource.com/chromium/src.git/+/master/docs/testing/rendering_representative_perf_tests.md#updating-expectations
it is better to mark them as experimental rather than skip them.

This CL addresses that issue, and marks them as experimental.

Bug: 1122037
Change-Id: Iae875773d08d101c6fffb4b274780520f530a8d2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2401337Reviewed-by: Behdad Bakhshinategh <behdadb@chromium.org>
Reviewed-by: Yi Xu <yiyix@chromium.org>
Reviewed-by: John Chen <johnchen@chromium.org>
Reviewed-by: Juanmi Huertas <juanmihd@chromium.org>
Commit-Queue: Behdad Bakhshinategh <behdadb@chromium.org>
Auto-Submit: Juanmi Huertas <juanmihd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805745}

testing/scripts/representative_perf_test_data/representatives_frame_times_upper_limit.json

@@ -86,7 +86,9 @@
     "balls_javascript_canvas": {
       "ci_095": 1.324,
       "avg": 39.475,
-      "cpu_wall_time_ratio": 0.556
+      "cpu_wall_time_ratio": 0.556,
+      "experimental": true,
+      "_comment": "crbug.com/1122037"
     },
     "transform_transitions_js_block": {
       "ci_095": 0.366,
@@ -101,7 +103,9 @@
     "fill_shapes": {
       "ci_095": 0.949,
       "avg": 32.306,
-      "cpu_wall_time_ratio": 0.539
+      "cpu_wall_time_ratio": 0.539,
+      "experimental": true,
+      "_comment": "crbug.com/1122037"
     },
     "css_value_type_shadow": {
       "ci_095": 18.3,

tools/perf/expectations.config

@@ -200,8 +200,6 @@ crbug.com/755556 [ mac ] rendering.desktop/mix_blend_mode_animation_hue [ Skip ]
 crbug.com/1017244 [ desktop ] rendering.desktop/youtube_2018 [ Skip ]
 crbug.com/1017244 [ desktop ] rendering.desktop/youtube_pinch_2018 [ Skip ]
 crbug.com/1044962 [ win ] rendering.desktop/camera_to_webgl [ Skip ]
-crbug.com/1122037 [ mac ] rendering.desktop/fill_shapes [ Skip ]
-crbug.com/1122037 [ mac ] rendering.desktop/balls_javascript_canvas [ Skip ]
 
 # Benchmark: rendering.mobile
 crbug.com/785485 [ android-webview ] rendering.mobile/kevs_3d [ Skip ]