Update in-product help experiment fieldtrial test downloading pages

This CL updates the testing configuration for the in-product help
feature for downloading web pages on Android after taking a
screenshot to the planned launch configuration.

BUG=748574

Change-Id: Iee3f04274649c62d3476539bd04441e6730fbd18
Reviewed-on: https://chromium-review.googlesource.com/884985Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Tommy Nyquist <nyquist@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532074}

testing/variations/fieldtrial_testing_config.json

@@ -324,13 +324,14 @@
             ],
             "experiments": [
                 {
-                    "name": "Tracking",
+                    "name": "EnabledTracking",
                     "params": {
-                        "availability": ">=14",
-                        "event_1": "name:screenshot_taken_chrome_in_foreground;comparator:>=1;window:135;storage:360",
-                        "event_trigger": "name:download_page_iph_trigger;comparator:==0;window:90;storage:360",
-                        "event_used": "name:download_page_started;comparator:==0;window:135;storage:360",
-                        "session_rate": "<0"
+                        "availability": "any",
+                        "event_screenshot_taken": "name:screenshot_taken_chrome_in_foreground;comparator:>=1;window:90;storage:360",
+                        "event_trigger": "name:download_page_iph_would_have_triggered;comparator:==0;window:90;storage:360",
+                        "event_used": "name:download_page_started;comparator:==0;window:90;storage:360",
+                        "session_rate": "<=1",
+                        "tracking_only": "true"
                     },
                     "enable_features": [
                         "IPH_DownloadPageScreenshot"