Implement a modal permission dialog on Android gated by a feature.

chrome/common/chrome_features.cc

Index: chrome/common/chrome_features.cc
diff --git a/chrome/common/chrome_features.cc b/chrome/common/chrome_features.cc
index 8b3cd4068f12180901335e7f2bd402003e01e981..2dad452135cb89516776af3dcf788b5bad3d3069 100644
--- a/chrome/common/chrome_features.cc
+++ b/chrome/common/chrome_features.cc
@@ -114,6 +114,10 @@ const base::Feature kMaterialDesignHistory{
 const base::Feature kMaterialDesignSettings{
     "MaterialDesignSettings", base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Enables or disables modal permission prompts.
+const base::Feature kModalPermissionPrompts{"ModalPermissionPrompts",
+                                            base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Enables the use of native notification centers instead of using the Message
 // Center for displaying the toasts.
 #if defined(OS_MACOSX)