Disable Chromium's default PDF viewer infobar (#35556)

The kPdfInfoBar feature (enabled by default in Chromium) prompts users
to set Chrome as the default PDF viewer. Brave should not show this
Chrome-specific upsell.

app/feature_defaults_unittest.cc

@@ -166,6 +166,9 @@ TEST(FeatureDefaultsTest, DisabledFeatures) {
 #if BUILDFLAG(IS_WIN) || BUILDFLAG(IS_MAC) || BUILDFLAG(IS_LINUX)
       &features::kFewerUpdateConfirmations,
       &features::kShortcutsNotApps,
+#endif
+#if BUILDFLAG(IS_WIN) || BUILDFLAG(IS_MAC)
+      &features::kPdfInfoBar,
 #endif
       &features::kHttpsFirstBalancedMode,
       &features::kIdleDetection,

chromium_src/chrome/browser/ui/ui_features.cc

@@ -14,6 +14,10 @@ namespace features {
 OVERRIDE_FEATURE_DEFAULT_STATES({{
 #if BUILDFLAG(IS_WIN) || BUILDFLAG(IS_MAC) || BUILDFLAG(IS_LINUX)
     {kFewerUpdateConfirmations, base::FEATURE_DISABLED_BY_DEFAULT},
+#endif
+#if BUILDFLAG(IS_WIN) || BUILDFLAG(IS_MAC)
+    // PDF infobar is only used on Windows and macOS upstream.
+    {kPdfInfoBar, base::FEATURE_DISABLED_BY_DEFAULT},
 #endif
     // TODO(https://github.com/brave/brave-browser/issues/46337): Re-enable
     // scrim views if needed.

test/filters/unit_tests.filter

@@ -5,6 +5,9 @@
 ## why the filter is required and create an associated tracking issue.
 ##
 
+# Tests assume kPdfInfoBar is enabled; we disable it.
+-PdfInfoBarControllerTest.*
+
 # These tests won't work without TPM hardware
 -TPMMetricsProviderTest.GetMetricsFullName
 -TpmIdentifierTest.TpmTest