Write skia_unittests.isolate and enable swarming for skia_unittests.

testing/buildbot/chromium.memory.fyi.json

Index: testing/buildbot/chromium.memory.fyi.json
diff --git a/testing/buildbot/chromium.memory.fyi.json b/testing/buildbot/chromium.memory.fyi.json
index 5a41bc133dfa8ecabcc3c2a8a6864fc101a63a9f..f75475c01a192d69cccf71b23df50ffab4cdbedf 100644
--- a/testing/buildbot/chromium.memory.fyi.json
+++ b/testing/buildbot/chromium.memory.fyi.json
@@ -181,6 +181,9 @@
         "test": "sandbox_linux_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "skia_unittests"
       },
       {
@@ -396,6 +399,9 @@
         "test": "sandbox_linux_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "skia_unittests"
       },
       {
@@ -578,6 +584,9 @@
         "test": "sandbox_linux_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "skia_unittests"
       },
       {