Add WebSocketReassembleShortMessages config

Add WebSocketReassembleShortMessages to fieldtrial_testing_config.json
to make Finch happy about the upcoming beta trial.

BUG=1086273

Change-Id: I04292429d1c676efb0ff99eb9d16f940e135e62f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2277695Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#785709}

testing/variations/fieldtrial_testing_config.json

@@ -7926,6 +7926,26 @@
             ]
         }
     ],
+    "WebSocketReassembleShortMessages": [
+        {
+            "platforms": [
+                "android",
+                "android_webview",
+                "chromeos",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "DisabledBeta",
+                    "disable_features": [
+                        "WebSocketReassembleShortMessages"
+                    ]
+                }
+            ]
+        }
+    ],
     "WebUITabStrip": [
         {
             "platforms": [