[signin] Force light mode in the reauth dialog

To force the light mode on the Reauth confirmation screen, we override
the preferred_color_scheme web preference in SigninReauthViewController.
However, a web preference overridden via WebContents::SetWebPreferences
doesn't survive a recomputation of WebPreferences. This means that the
preferred_color_scheme returns back to its default value.

The comment to the SetWebPreferences method suggests to put the
recomputation logic in ChromeContentBrowserClient. This CL does exactly
that.

This CL also adds a browser test to verify the behavior and catch
possible regressions.

Bug: 1153368
Change-Id: I8697e13095ba58d120f6ce61352caa32a982be0d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2565684
Commit-Queue: Alex Ilin <alexilin@chromium.org>
Reviewed-by: David Roger <droger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832324}

chrome/browser/chrome_content_browser_client.cc

@@ -2984,21 +2984,26 @@ bool UpdatePreferredColorScheme(WebPreferences* web_prefs,
       ToBlinkPreferredColorScheme(native_theme->GetPreferredColorScheme());
 #endif  // defined(OS_ANDROID)
 
+  bool force_light = false;
   // Force a light preferred color scheme on certain URLs if kWebUIDarkMode is
   // disabled; some of the UI is not yet correctly themed.
   if (!base::FeatureList::IsEnabled(features::kWebUIDarkMode)) {
     // Update based on last committed url.
-    bool force_light = url.SchemeIs(content::kChromeUIScheme);
+    force_light |= url.SchemeIs(content::kChromeUIScheme);
 #if BUILDFLAG(ENABLE_EXTENSIONS)
-    if (!force_light) {
-      force_light = url.SchemeIs(extensions::kExtensionScheme) &&
-                    url.host_piece() == extension_misc::kPdfExtensionId;
-    }
+    force_light |= url.SchemeIs(extensions::kExtensionScheme) &&
+                   url.host_piece() == extension_misc::kPdfExtensionId;
 #endif
-    if (force_light) {
-      web_prefs->preferred_color_scheme =
-          blink::mojom::PreferredColorScheme::kLight;
-    }
+  }
+
+  // Reauth WebUI doesn't support dark mode yet because it shares the dialog
+  // with GAIA web contents that is not correctly themed.
+  force_light |= url.SchemeIs(content::kChromeUIScheme) &&
+                 url.host_piece() == chrome::kChromeUISigninReauthHost;
+
+  if (force_light) {
+    web_prefs->preferred_color_scheme =
+        blink::mojom::PreferredColorScheme::kLight;
   }
 
   return old_preferred_color_scheme != web_prefs->preferred_color_scheme;

chrome/browser/ui/signin_reauth_view_controller.cc

@@ -29,8 +29,6 @@
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "google_apis/gaia/gaia_urls.h"
-#include "third_party/blink/public/common/web_preferences/web_preferences.h"
-#include "third_party/blink/public/mojom/css/preferred_color_scheme.mojom.h"
 
 namespace {
 
@@ -311,15 +309,10 @@ void SigninReauthViewController::ShowReauthConfirmationDialog() {
           browser_, account_id_, access_point_);
   dialog_delegate_observer_.Add(dialog_delegate_);
 
-  // Gaia Reauth page doesn't support dark mode. Force the confirmation dialog
-  // to use the light mode as well to match the style.
-  auto* web_contents = dialog_delegate_->GetWebContents();
-  auto prefs = web_contents->GetOrCreateWebPreferences();
-  prefs.preferred_color_scheme = blink::mojom::PreferredColorScheme::kLight;
-  web_contents->SetWebPreferences(prefs);
-
-  SigninReauthUI* web_dialog_ui =
-      web_contents->GetWebUI()->GetController()->GetAs<SigninReauthUI>();
+  SigninReauthUI* web_dialog_ui = dialog_delegate_->GetWebContents()
+                                      ->GetWebUI()
+                                      ->GetController()
+                                      ->GetAs<SigninReauthUI>();
   web_dialog_ui->InitializeMessageHandlerWithReauthController(this);
 }
 

chrome/browser/ui/signin_reauth_view_controller_browsertest.cc

@@ -12,6 +12,7 @@
 #include "base/test/bind.h"
 #include "base/test/metrics/histogram_tester.h"
 #include "base/test/mock_callback.h"
+#include "base/test/scoped_feature_list.h"
 #include "chrome/browser/signin/identity_manager_factory.h"
 #include "chrome/browser/signin/reauth_result.h"
 #include "chrome/browser/signin/signin_features.h"
@@ -19,6 +20,7 @@
 #include "chrome/browser/ui/signin_reauth_view_controller.h"
 #include "chrome/browser/ui/signin_view_controller.h"
 #include "chrome/browser/ui/webui/signin/login_ui_test_utils.h"
+#include "chrome/common/chrome_features.h"
 #include "chrome/test/base/in_process_browser_test.h"
 #include "chrome/test/base/ui_test_utils.h"
 #include "components/signin/public/base/signin_metrics.h"
@@ -38,6 +40,7 @@
 #include "net/test/embedded_test_server/embedded_test_server.h"
 #include "net/test/embedded_test_server/http_response.h"
 #include "net/test/embedded_test_server/request_handler_util.h"
+#include "ui/base/ui_base_switches.h"
 
 using ::testing::ElementsAre;
 
@@ -541,3 +544,39 @@ IN_PROC_BROWSER_TEST_F(SigninReauthViewControllerBrowserTest,
       browser(), kReauthDialogTimeout));
   EXPECT_EQ(WaitForReauthResult(), signin::ReauthResult::kUnexpectedResponse);
 }
+
+class SigninReauthViewControllerDarkModeBrowserTest
+    : public SigninReauthViewControllerBrowserTest {
+ public:
+  SigninReauthViewControllerDarkModeBrowserTest() {
+    scoped_feature_list_.InitAndEnableFeature(features::kWebUIDarkMode);
+  }
+
+  void SetUpCommandLine(base::CommandLine* command_line) override {
+    command_line->AppendSwitch(switches::kForceDarkMode);
+    SigninReauthViewControllerBrowserTest::SetUpCommandLine(command_line);
+  }
+
+ private:
+  base::test::ScopedFeatureList scoped_feature_list_;
+};
+
+// Tests the light mode is enforced for the reauth confirmation dialog even if
+// the dark mode is enabled.
+IN_PROC_BROWSER_TEST_F(SigninReauthViewControllerDarkModeBrowserTest,
+                       ConfirmationDialogDarkModeDisabled) {
+  ShowReauthPrompt();
+  content::WebContents* confirmation_dialog_contents =
+      signin_reauth_view_controller()->GetWebContents();
+  content::TestNavigationObserver navigation_observer(
+      confirmation_dialog_contents);
+  navigation_observer.WaitForNavigationFinished();
+
+  bool prefers_dark_mode = true;
+  EXPECT_TRUE(content::ExecuteScriptAndExtractBool(
+      confirmation_dialog_contents,
+      "window.domAutomationController.send("
+      "window.matchMedia('(prefers-color-scheme: dark)').matches)",
+      &prefers_dark_mode));
+  EXPECT_EQ(prefers_dark_mode, false);
+}