Add field trial config for AndroidWideColorGamut

Android uses the dynamic color gamut to change gamuts as needed based
on the content being displayed. There is a Finch experiment for this
which is rolled out to 50% of Canary and Dev channels.

This CL adds a field trial for that Finch experiment so bots can test
the config.

Change-Id: I112a9dc0f8edb99b39f227a81a7785527717db95
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2225622
Commit-Queue: Chris Blume <cblume@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774393}

testing/variations/fieldtrial_testing_config.json

@@ -109,6 +109,21 @@
             ]
         }
     ],
+    "AndroidDynamicWideColorGamut": [
+        {
+            "platforms": [
+                "android"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "DynamicColorGamut"
+                    ]
+                }
+            ]
+        }
+    ],
     "AndroidInProductHelpContextualSearchPromotePanelOpen": [
         {
             "platforms": [