fix: re-enable MacWebContentsOcclusion feature flag (#45801)

Co-authored-by: trop[bot] <37223003+trop[bot]@users.noreply.github.com>
Co-authored-by: Keeley Hammond <khammond@slack-corp.com>

shell/browser/feature_list.cc

@@ -11,6 +11,7 @@
 #include "base/feature_list.h"
 #include "base/metrics/field_trial.h"
 #include "components/spellcheck/common/spellcheck_features.h"
+#include "content/common/features.h"
 #include "content/public/common/content_features.h"
 #include "electron/buildflags/buildflags.h"
 #include "media/base/media_switches.h"
@@ -48,6 +49,13 @@ void InitializeFeatureList() {
       std::string(",") + spellcheck::kWinDelaySpellcheckServiceInit.name;
 #endif
 
+#if BUILDFLAG(IS_MAC)
+  disable_features +=
+      // MacWebContentsOcclusion is causing some odd visibility
+      // issues with multiple web contents
+      std::string(",") + features::kMacWebContentsOcclusion.name;
+#endif
+
 #if BUILDFLAG(ENABLE_PDF_VIEWER)
   // Enable window.showSaveFilePicker api for saving pdf files.
   // Refs https://issues.chromium.org/issues/373852607