Enable WebViewFasterGetDefaultUserAgent by default

patches/0267-Enable-WebViewFasterGetDefaultUserAgent-by-default.patch

@@ -0,0 +1,61 @@
+From 1948eb6ea786ec7e7efb1f8dbc764ee509030b96 Mon Sep 17 00:00:00 2001
+From: inthewaves <inthewaves@pm.me>
+Date: Fri, 22 May 2026 01:35:30 -0700
+Subject: [PATCH 267/267] Enable WebViewFasterGetDefaultUserAgent by default
+
+Apps, in particular ones that use Google Mobile Ads SDK, can dead lock. A worker thread in the
+Mobile Ads SDK holds a singleton lock and calls WebSettings.getDefaultUserAgent() which block until
+a task posted to the main thread to initialize WebView finishes. Meanwhile, the main thread of the
+app enters Mobile Ads SDK. If the Dynamite ads module is not available, the library has a local
+fallback path which attempts to acquires the singleton lock that the worker thread is holding. The
+result is that the main thread gets blocked on a lock held by the worker thread which is waiting for
+main thread to process its task.
+
+Dynamite ads module can be unavailable if Play services + Play Store are not installed (or have some
+other issue). This would block users from using any app with SDK used in this way.
+
+By enabling this feature, the worker thread no longer waits on the initialization task posted to
+main thread to finish and gets a user agent immediately. This works around this deadlock.
+
+Note that Vanadium config doesn't handle WebViewCachedFlags which is meant to be fast and designed
+around SharedPreferences. The feature is only read in the relevant location from WebViewCachedFlags,
+so the native feature change is just for completeness.
+
+Test: Install app like com.faitaujapon.otg which had this issue. With no Play services install, app
+no longer ANRs on start
+Test: tools/autotest.py -C out/Default \
+  android_webview/tools/system_webview_shell/layout_tests/src/org/chromium/webview_shell/test/WebViewThreadTest.java
+---
+ android_webview/common/aw_features.cc                           | 2 +-
+ .../org/chromium/android_webview/common/WebViewCachedFlags.java | 2 +-
+ 2 files changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/android_webview/common/aw_features.cc b/android_webview/common/aw_features.cc
+index 337eb3d747457..5b06bf14955c3 100644
+--- a/android_webview/common/aw_features.cc
++++ b/android_webview/common/aw_features.cc
+@@ -306,7 +306,7 @@ BASE_FEATURE(kWebViewUseNonembeddedLowEntropySource,
+ // When enabled, the default user agent string is fetched more quickly without
+ // waiting for chromium startup to complete.
+ BASE_FEATURE(kWebViewFasterGetDefaultUserAgent,
+-             base::FEATURE_DISABLED_BY_DEFAULT);
++             base::FEATURE_ENABLED_BY_DEFAULT);
+
+ // When enabled, navigation headers will be saved and restored as part
+ // of saved state for WebView.
+diff --git a/android_webview/java/src/org/chromium/android_webview/common/WebViewCachedFlags.java b/android_webview/java/src/org/chromium/android_webview/common/WebViewCachedFlags.java
+index ebc8767f55788..fda0e693177c8 100644
+--- a/android_webview/java/src/org/chromium/android_webview/common/WebViewCachedFlags.java
++++ b/android_webview/java/src/org/chromium/android_webview/common/WebViewCachedFlags.java
+@@ -180,7 +180,7 @@ public class WebViewCachedFlags {
+                                             DefaultState.DISABLED),
+                                     Map.entry(
+                                             AwFeatures.WEBVIEW_FASTER_GET_DEFAULT_USER_AGENT,
+-                                            DefaultState.DISABLED),
++                                            DefaultState.ENABLED),
+                                     Map.entry(
+                                             BaseFeatures
+                                                     .SHUTDOWN_PRE_NATIVE_THREAD_POOL_AFTER_STARTUP,
+-- 
+2.43.0
+