Turn on OOP Raster on android bots

This still has one known perf issue (frame time / input latency jank),
but this is due to long shader compilation causing delayed display
compositing.  However, no short term solution will fix bots that
clobber the shader cache between every run, and so smoothness tests will
regress cold start no matter what we do in the short term even if this
is not what most users will see.

Therefore, it seems like this is ready to turn on for the bots and
flush out any unknown issues that we haven't found yet.

Bug: 757605
Change-Id: I29249946e1b91d890b9ee677b4941dd8b8507abd
Reviewed-on: https://chromium-review.googlesource.com/1117275Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: enne <enne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571694}

testing/variations/fieldtrial_testing_config.json

@@ -1249,6 +1249,21 @@
             ]
         }
     ],
+    "DefaultEnableOopRasterization": [
+        {
+            "platforms": [
+                "android"
+            ],
+            "experiments": [
+                {
+                    "name": "DefaultEnableOopRasterization",
+                    "enable_features": [
+                        "DefaultEnableOopRasterization"
+                    ]
+                }
+            ]
+        }
+    ],
     "DefaultPassthroughCommandDecoder": [
         {
             "platforms": [