Hardcode extensions::util::IsNewBookmarkAppsEnabled() to true, except on Mac.

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 bdbb9a92d6c858069d783d92cd8da3121c16eced..45b9b86b732f637d94992749f539e0fba805a246 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -99203,6 +99203,7 @@ from previous Chrome versions.
   <int value="-86788587" label="allow-autofill-sync-credential"/>
   <int value="-80353187" label="disable-display-color-calibration"/>
   <int value="-78035185" label="custom_summary"/>
+  <int value="-77872983" label="BookmarkAppsMac:disabled"/>
   <int value="-76631048" label="disable-offline-auto-reload-visible-only"/>
   <int value="-70595606" label="ash-enable-unified-desktop"/>
   <int value="-68877684" label="BackgroundVideoTrackOptimization:enabled"/>
@@ -99273,6 +99274,7 @@ from previous Chrome versions.
   <int value="262382944" label="GuestViewCrossProcessFrames:disabled"/>
   <int value="266702296" label="disable-plugin-power-saver"/>
   <int value="270267831" label="enable-scripts-require-action"/>
+  <int value="272631627" label="BookmarkAppsMac:enabled"/>
   <int value="274103741" label="enable-ntp-popular-sites"/>
   <int value="278756320" label="disable-app-list-app-info"/>
   <int value="280644887" label="mash"/>