ContentCapture: Enabled in field trial

ContentCapture was triggered by ContentCaptureConsumer, the
ContentCaptureTriggeringForExperiment feature is used to trigger the
ContentCapture independently, so we can get unbiased experiment
result.

We enabled this feature to run an experiment in M86. Now we need
to disable it to prevent ContentCapture being triggered
unconditionally in production in M87 and beyond.

By disabling this feature, ContentCapture will lack the test coverage
because it isn't triggered.

To overcome this issue, this patch enables experiment in fieldtrial
and disabled ContentCapture by default in production, so it is only
triggered when necessary in production, but we still have enough test
coverage in various bots.

Also, removed an unused fieldtrial setting.

Bug: 1114819
Change-Id: I9c2a5c5dcea9697020b372cef660289c42243470
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2422148Reviewed-by: Brian White <bcwhite@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Michael Bai <michaelbai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809673}

components/content_capture/common/content_capture_features.cc

@@ -16,7 +16,7 @@ const base::Feature kContentCapture{"ContentCapture",
                                     base::FEATURE_ENABLED_BY_DEFAULT};
 
 const base::Feature kContentCaptureTriggeringForExperiment{
-    "ContentCaptureTriggeringForExperiment", base::FEATURE_ENABLED_BY_DEFAULT};
+    "ContentCaptureTriggeringForExperiment", base::FEATURE_DISABLED_BY_DEFAULT};
 #else
 const base::Feature kContentCapture{"ContentCapture",
                                     base::FEATURE_DISABLED_BY_DEFAULT};

testing/variations/fieldtrial_testing_config.json

@@ -1734,7 +1734,7 @@
             ]
         }
     ],
-    "ContentCapture": [
+    "ContentCaptureExperiment": [
         {
             "platforms": [
                 "android",
@@ -1743,14 +1743,9 @@
             ],
             "experiments": [
                 {
-                    "name": "ContentCaptureUseTextHolder",
-                    "params": {
-                        "task_long_delay_in_milliseconds": "5000",
-                        "task_short_delay_in_milliseconds": "500",
-                        "use_node_id": "false"
-                    },
+                    "name": "EnableExperiment",
                     "enable_features": [
-                        "ContentCapture"
+                        "ContentCaptureTriggeringForExperiment"
                     ]
                 }
             ]