Added field trial for enabling AppContainer and a chrome://flags entry.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index b317a7d0bc497e2fc1f3744f2ca08b50df52775e..fa82464f3a2b04f3abcfb60eb5295ac25c724f40 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -65097,6 +65097,7 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="-1319688939" label="ignore-gpu-blacklist"/>
   <int value="-1302904242" label="enable-navigation-tracing"/>
   <int value="-1285021473" label="save-page-as-mhtml"/>
+  <int value="-1271563519" label="enable-appcontainer"/>
   <int value="-1268836676" label="disable-out-of-process-pdf"/>
   <int value="-1267958145" label="disable-pdf-material-ui"/>
   <int value="-1251411236" label="disable-new-md-input-view"/>
@@ -65295,6 +65296,7 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="460475728" label="wake-on-wifi-packet"/>
   <int value="466248382" label="disable-push-api-background-mode"/>
   <int value="474743272" label="material-design-ink-drop"/>
+  <int value="493903641" label="disable-appcontainer"/>
   <int value="494733611" label="disable-drop-sync-credential"/>
   <int value="503245473" label="disable-translate-new-ux"/>
   <int value="535976218" label="enable-plugin-power-saver"/>