[Android WebView] Fix thread unsafety in accessing Java side getters

android_webview/native/aw_settings.cc

Index: android_webview/native/aw_settings.cc
diff --git a/android_webview/native/aw_settings.cc b/android_webview/native/aw_settings.cc
index 13c7f0879fca577eecf784776f3dc0db70999fc2..cb2cbf1e500003a0d32ad8f491f4bdda7dc2a557 100644
--- a/android_webview/native/aw_settings.cc
+++ b/android_webview/native/aw_settings.cc
@@ -188,14 +188,20 @@ void AwSettings::PopulateFixedPreferences(WebPreferences* web_prefs) {
 void AwSettings::PopulateWebPreferences(WebPreferences* web_prefs) {
   JNIEnv* env = base::android::AttachCurrentThread();
   CHECK(env);
-
-  AwRenderViewHostExt* render_view_host_ext = GetAwRenderViewHostExt();
-  if (!render_view_host_ext) return;
-
   ScopedJavaLocalRef<jobject> scoped_obj = aw_settings_.get(env);
   jobject obj = scoped_obj.obj();
   if (!obj) return;
+  // Grab the lock and call PopulateWebPreferencesLocked.
+  Java_AwSettings_populateWebPreferences(
+      env, obj, reinterpret_cast<jlong>(web_prefs));
+}
+
+void AwSettings::PopulateWebPreferencesLocked(
+    JNIEnv* env, jobject obj, jlong web_prefs_ptr) {
+  AwRenderViewHostExt* render_view_host_ext = GetAwRenderViewHostExt();
+  if (!render_view_host_ext) return;
 
+  WebPreferences* web_prefs = reinterpret_cast<WebPreferences*>(web_prefs_ptr);
   PopulateFixedPreferences(web_prefs);
 
   web_prefs->text_autosizing_enabled =