Cache all flags enabled in ServiceManager only mode when native is loaded.

This is a follow up CL for https://crrev.com/c/1758500. In this CL, caching the
native flags is called when native is loaded in ServiceManager only mode,
including:
- ServiceManagerForDownload
- ServiceManagerForBackgroundPrefetch

Bug: 984559,995355
Change-Id: I51b00b3be048dc6ec377eeef0f81bbc0ce4e9023
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1759682
Commit-Queue: Xi Han <hanxi@chromium.org>
Reviewed-by: Henrique Nakashima <hnakashima@chromium.org>
Reviewed-by: Carlos Knippschild <carlosk@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688198}

chrome/android/java/src/org/chromium/chrome/browser/init/ChromeBrowserInitializer.java

@@ -37,6 +37,7 @@ import org.chromium.chrome.browser.FileProviderHelper;
 import org.chromium.chrome.browser.crash.LogcatExtractionRunnable;
 import org.chromium.chrome.browser.download.DownloadManagerService;
 import org.chromium.chrome.browser.services.GoogleServicesManager;
+import org.chromium.chrome.browser.util.FeatureUtilities;
 import org.chromium.chrome.browser.webapps.ActivityAssigner;
 import org.chromium.chrome.browser.webapps.ChromeWebApkHost;
 import org.chromium.components.background_task_scheduler.BackgroundTaskSchedulerExternalUma;
@@ -438,6 +439,9 @@ public class ChromeBrowserInitializer {
         // TODO(crbug.com/960767): Remove this in M77.
         ServiceManagerStartupUtils.cleanupSharedPreferences();
 
+        // Needed for field trial metrics to be properly collected in ServiceManager only mode.
+        FeatureUtilities.cacheNativeFlagsForServiceManagerOnlyMode();
+
         PostTask.postTask(
                 TaskTraits.BEST_EFFORT_MAY_BLOCK, LibraryPrefetcher::maybePinOrderedCodeInMemory);
     }

chrome/android/java/src/org/chromium/chrome/browser/offlinepages/prefetch/PrefetchBackgroundTask.java

@@ -90,23 +90,12 @@ public class PrefetchBackgroundTask extends NativeBackgroundTask {
         sAlwaysSupportServiceManagerOnlyForTesting = true;
     }
 
-    @VisibleForTesting
-    static void skipCachingFlagForTesting() {
-        sSkipCachingFlagForTesting = true;
-    }
-
     @Override
     protected void onStartTaskWithNative(
             Context context, TaskParameters taskParameters, TaskFinishedCallback callback) {
         assert taskParameters.getTaskId() == TaskIds.OFFLINE_PAGES_PREFETCH_JOB_ID;
         if (mNativeTask != 0) return;
 
-        // Caches the flag. If a field trial isn't explicitly checked in the code, it won't be
-        // tagged as active. This might cause many UMA data of "Servicification.Startup2" are shown
-        // in the "not in study" bucket.
-        if (!sSkipCachingFlagForTesting)
-            FeatureUtilities.cacheServiceManagerForBackgroundPrefetch();
-
         // Only Feed is supported in reduced mode.
         // If we launched chrome in reduced mode but it turns out that Feed is not enabled (because
         // the cached value of the flag was stale), we should cache the new value and reschedule

chrome/android/java/src/org/chromium/chrome/browser/util/FeatureUtilities.java

@@ -186,8 +186,6 @@ public class FeatureUtilities {
         cacheDownloadAutoResumptionEnabledInNative();
         cachePrioritizeBootstrapTasks();
         cacheFeedEnabled();
-        cacheServiceManagerForDownloadResumption();
-        cacheServiceManagerForBackgroundPrefetch();
         cacheNetworkServiceWarmUpEnabled();
         cacheImmersiveUiModeEnabled();
         cacheSwapPixelFormatToFixConvertFromTranslucentEnabled();
@@ -202,6 +200,18 @@ public class FeatureUtilities {
                 ChromeFeatureList.isEnabled(ChromeFeatureList.REACHED_CODE_PROFILER));
     }
 
+    /**
+     * Caches flags that are enabled in ServiceManager only mode and must take effect on startup but
+     * are set via native code. This function needs to be called in ServiceManager only mode to mark
+     * these field trials as active, otherwise histogram data recorded in ServiceManager only mode
+     * won't be tagged with their corresponding field trial experiments.
+     */
+    public static void cacheNativeFlagsForServiceManagerOnlyMode() {
+        // TODO(crbug.com/995355): Move other related flags from {@link cacheNativeFlags} to here.
+        cacheServiceManagerForDownloadResumption();
+        cacheServiceManagerForBackgroundPrefetch();
+    }
+
     /**
      * @return True if tab model merging for Android N+ is enabled.
      */

chrome/android/junit/src/org/chromium/chrome/browser/offlinepages/prefetch/PrefetchBackgroundTaskUnitTest.java

@@ -133,8 +133,6 @@ public class PrefetchBackgroundTaskUnitTest {
 
         mFakeTaskScheduler = new FakeBackgroundTaskScheduler();
         BackgroundTaskSchedulerFactory.setSchedulerForTesting(mFakeTaskScheduler);
-
-        PrefetchBackgroundTask.skipCachingFlagForTesting();
     }
 
     @Test