[cr135] Disables kExtensionManifestV2Disabled feature.

Chromium change:

https://source.chromium.org/chromium/chromium/src/+/400a8f16a7e49a5de696a94405aad97f3e649570

commit 400a8f16a7e49a5de696a94405aad97f3e649570
Author: Devlin Cronin <rdevlin.cronin@chromium.org>
Date:   Tue Feb 18 10:49:00 2025 -0800

    [Extensions MV2] Enable kExtensionManifestV2Disabled by default

    Chrome has announced that MV2 extensions will gradually no longer be
    supported in the browser. See more information at
    https://developer.chrome.com/blog/resuming-the-transition-to-mv3.

    This enables the kExtensionManifestV2Disabled base::Feature by default.
    This has been gradually rolled out to existing user populations. Users
    may still re-enable MV2 extensions during this time.

    Bug: 337191307

app/feature_defaults_unittest.cc

@@ -121,6 +121,7 @@ TEST(FeatureDefaultsTest, DisabledFeatures) {
 #if !BUILDFLAG(IS_ANDROID)
       &enterprise_signals::features::kDeviceSignalsConsentDialog,
       &extensions_features::kExtensionManifestV2DeprecationWarning,
+      &extensions_features::kExtensionManifestV2Disabled,
       &extensions_features::kExtensionManifestV2Unsupported,
       &extensions_features::kExtensionsManifestV3Only,
 #endif

chromium_src/extensions/common/extension_features.cc

@@ -11,6 +11,7 @@ namespace extensions_features {
 
 OVERRIDE_FEATURE_DEFAULT_STATES({{
     {kExtensionManifestV2DeprecationWarning, base::FEATURE_DISABLED_BY_DEFAULT},
+    {kExtensionManifestV2Disabled, base::FEATURE_DISABLED_BY_DEFAULT},
     {kExtensionManifestV2Unsupported, base::FEATURE_DISABLED_BY_DEFAULT},
     {kExtensionsManifestV3Only, base::FEATURE_DISABLED_BY_DEFAULT},
 }});