DPWA: add fieldtrial testing for install icon IPH

Add fieldtrial test configuration for Desktop PWA install icon
In-Product Help finch experiment.

Change-Id: Ida43f4ed7a173dcfc1794d8d945fad6842fd46ed
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2594264Reviewed-by: Phillis Tang <phillis@chromium.org>
Reviewed-by: Caitlin Fischer <caitlinfischer@google.com>
Commit-Queue: Phillis Tang <phillis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837790}

testing/variations/fieldtrial_testing_config.json

@@ -2381,6 +2381,31 @@
             ]
         }
     ],
+    "DesktopPwaInstallInProductHelp": [
+        {
+            "platforms": [
+                "chromeos",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "params": {
+                        "availability": "any",
+                        "event_trigger": "name:desktop_pwa_install_iph_triggered;comparator:any;window:90;storage:365",
+                        "event_used": "name:desktop_pwa_installed;comparator:any;window:90;storage:365",
+                        "session_rate": "==0",
+                        "x_site_engagement_threshold": "10"
+                    },
+                    "enable_features": [
+                        "IPH_DesktopPwaInstall"
+                    ]
+                }
+            ]
+        }
+    ],
     "DesktopTabGroupsCollapse": [
         {
             "platforms": [