Write skia_unittests.isolate and enable swarming for skia_unittests.

testing/buildbot/chromium.memory.json

Index: testing/buildbot/chromium.memory.json
diff --git a/testing/buildbot/chromium.memory.json b/testing/buildbot/chromium.memory.json
index 1897453e73d48a84d8d90da51590d3be5dd727a1..e0d268047f6394aa86011754cf843840bbac2a71 100644
--- a/testing/buildbot/chromium.memory.json
+++ b/testing/buildbot/chromium.memory.json
@@ -140,6 +140,9 @@
         "test": "sandbox_linux_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "skia_unittests"
       },
       {
@@ -348,6 +351,9 @@
         "test": "sandbox_linux_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "skia_unittests"
       },
       {
@@ -485,6 +491,9 @@
         "test": "remoting_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "skia_unittests"
       },
       {