Enable arc-file-picker-experiment flag by default for M76

This means using CrOS file selector as default Android file picker
go/arc-file-selector

Bug: 64281746
Test: atest android.appsecurity.cts.DocumentsTest
Change-Id: Ie6f9e5319830b80da1d7a74e164945ef90ece9d3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1608864Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Commit-Queue: Satoshi Niwa <niwa@chromium.org>
Auto-Submit: Satoshi Niwa <niwa@chromium.org>
Cr-Commit-Position: refs/heads/master@{#658974}

components/arc/arc_features.cc

@@ -45,7 +45,7 @@ const base::Feature kEnableUnifiedAudioFocusFeature{
 
 // Controls experimental file picker feature for ARC.
 const base::Feature kFilePickerExperimentFeature{
-    "ArcFilePickerExperiment", base::FEATURE_DISABLED_BY_DEFAULT};
+    "ArcFilePickerExperiment", base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Controls experimental ARC graphic buffers visualization tools.
 const base::Feature kGraphicBuffersVisualizationTool{