Create field trial for wide color gamut on Pixel 4

The Pixel 4 supports wide color gamut. There is already a roll-out
in place to test wide color gamut on the Pixel 4.

This CL adds a field trial to match that roll-out.

R=isherman@chromium.org

Change-Id: Ibf678bf497aafa05b620b8e4e0750713ecfc2288
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1922458Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Chris Blume <cblume@chromium.org>
Cr-Commit-Position: refs/heads/master@{#716446}

testing/variations/fieldtrial_testing_config.json

@@ -583,6 +583,24 @@
             ]
         }
     ],
+    "AndroidWideColorGamut": [
+        {
+            "platforms": [
+                "android"
+            ],
+            "experiments": [
+                {
+                    "name": "UseDisplayWideColorGamut",
+                    "params": {
+                        "enabled_models": "Pixel 4,Pixel 4 XL"
+                    },
+                    "enable_features": [
+                        "UseDisplayWideColorGamut"
+                    ]
+                }
+            ]
+        }
+    ],
     "AppLauncherRefresh": [
         {
             "platforms": [