Create the base Custom Context Menu Dialog.

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 9e07aab99565dad319f056ae719b88866f574a54..f7e95e6b6b5815bcdc3221f0fba7e904d0638a81 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -2416,6 +2416,12 @@ const FeatureEntry kFeatureEntries[] = {
                                     kDelayNavigationFeatureVariations,
                                     "DelayNavigation")},
 
+#if defined(OS_ANDROID)
+    {"enable-custom-context-menu", IDS_FLAGS_ENABLE_CUSTOM_CONTEXT_MENU_NAME,
+     IDS_FLAGS_ENABLE_CUSTOM_CONTEXT_MENU_DESCRIPTION, kOsAndroid,
+     FEATURE_VALUE_TYPE(chrome::android::kCustomContextMenu)},
+#endif  // OS_ANDROID
+
     // NOTE: Adding new command-line switches requires adding corresponding
     // entries to enum "LoginCustomFlags" in histograms.xml. See note in
     // histograms.xml and don't forget to run AboutFlagsHistogramTest unit test.