Add Views implementation of ProfileSigninConfirmationDialog.

chrome/browser/ui/sync/profile_signin_confirmation_helper.cc

Index: chrome/browser/ui/sync/profile_signin_confirmation_helper.cc
diff --git a/chrome/browser/ui/sync/profile_signin_confirmation_helper.cc b/chrome/browser/ui/sync/profile_signin_confirmation_helper.cc
index 37e97bc01233af74406d197363f625968beacc83..a360a869846c2e4d72527ab93d9d637e67d55046 100644
--- a/chrome/browser/ui/sync/profile_signin_confirmation_helper.cc
+++ b/chrome/browser/ui/sync/profile_signin_confirmation_helper.cc
@@ -21,6 +21,8 @@
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/common/extensions/extension.h"
 #include "chrome/common/extensions/extension_set.h"
+#include "ui/gfx/color_utils.h"
+#include "ui/native_theme/native_theme.h"
 
 // TODO(dconnelly): change VLOG to DVLOG (crbug.com/240195)
 
@@ -200,6 +202,17 @@ void ProfileSigninConfirmationHelper::ReturnResult(bool result) {
 
 namespace ui {
 
+SkColor GetSigninConfirmationPromptBarColor(SkAlpha alpha) {
+  static const SkColor kBackgroundColor =
+      ui::NativeTheme::instance()->GetSystemColor(
+          ui::NativeTheme::kColorId_DialogBackground);
+  unsigned char background_luminance =
+      color_utils::GetLuminanceForColor(kBackgroundColor);
+  const SkColor blend_color =
+      background_luminance < 128 ? SK_ColorWHITE : SK_ColorBLACK;
+  return color_utils::AlphaBlend(blend_color, kBackgroundColor, alpha);
+}
+
 bool HasBeenShutdown(Profile* profile) {
   bool has_been_shutdown = !profile->IsNewProfile();
   if (has_been_shutdown)