Add flag for tablet mode double tap to zoom

The flag tracks a feature that is enabled by default,
which allows us to disable double-tap-to-zoom in the
future if we need to.

BUG=895574
TEST=Disable the feature and expect double-tap-to-zoom
     to stop working in tablet mode.

Change-Id: Ia3bafbb96ecd2fb55186b1fae388d955e34efb2f
Reviewed-on: https://chromium-review.googlesource.com/c/1281884
Reviewed-by: Scott Violet <[email protected]>
Commit-Queue: Ahmed Fakhry <[email protected]>
Cr-Commit-Position: refs/heads/master@{#599998}
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index 149dd22..aad4c470 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -3177,6 +3177,12 @@
 const char kDisableTabletSplitViewDescription[] =
     "Disable split view for Chrome OS tablet mode.";
 
+const char kDoubleTapToZoomInTabletModeName[] =
+    "Double-tap to zoom in tablet mode";
+const char kDoubleTapToZoomInTabletModeDescription[] =
+    "If Enabled, double tapping in webpages while in tablet mode will zoom the "
+    "page.";
+
 const char kEnableAppListSearchAutocompleteName[] =
     "App List Search Autocomplete";
 const char kEnableAppListSearchAutocompleteDescription[] =