[MacViews] Wire up AutofillPopupView

Added a "MacViewsAutofillPopup" feature flag and
--mac-views-autofill-popup switch. If it's enabled,
show the Autofill popup view using toolkit instead of
cocoa.

Removed AutofillPopupBaseView FocusManager accelerator code.
The code is no longer necessary since it was added for a now
obsolete rAc dialog. The autofill popup will get dismissed by
the web contents, which listens for the accelerators.

This is a reland of
https://chromium-review.googlesource.com/c/chromium/src/+/889983

The CL was reverted because of a crash (https://crbug.com/809830)
which was caused by the popup's container view's window set to
nil.

Bug: 728182
Change-Id: I02f74b5627e6559c4e4dd77a35860e77d000a0d5
Reviewed-on: https://chromium-review.googlesource.com/974106
Reviewed-by: Elly Fong-Jones <[email protected]>
Reviewed-by: Tommy Martino <[email protected]>
Reviewed-by: Trent Apted <[email protected]>
Reviewed-by: Evan Stade <[email protected]>
Commit-Queue: Sarah Chan <[email protected]>
Cr-Commit-Position: refs/heads/master@{#548270}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 4ca47720..478e95d 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -3783,6 +3783,12 @@
      flag_descriptions::kUsePdfCompositorServiceDescription, kOsDesktop,
      FEATURE_VALUE_TYPE(printing::features::kUsePdfCompositorServiceForPrint)},
 
+#if defined(OS_MACOSX)
+    {"mac-views-autofill-popup", flag_descriptions::kMacViewsAutofillPopupName,
+     flag_descriptions::kMacViewsAutofillPopupDescription, kOsMac,
+     FEATURE_VALUE_TYPE(autofill::kMacViewsAutofillPopup)},
+#endif  // OS_MACOSX
+
     {"autofill-dynamic-forms", flag_descriptions::kAutofillDynamicFormsName,
      flag_descriptions::kAutofillDynamicFormsDescription, kOsAll,
      FEATURE_VALUE_TYPE(autofill::features::kAutofillDynamicForms)},