[Cronet] Enable persistence mode for Sdch

components/cronet/android/url_request_context_adapter.cc

Index: components/cronet/android/url_request_context_adapter.cc
diff --git a/components/cronet/android/url_request_context_adapter.cc b/components/cronet/android/url_request_context_adapter.cc
index fd262c2ca6bac34b9480ddf32caf266818e5af58..1405b3003b3f3418c756a58282b18b5ef3785518 100644
--- a/components/cronet/android/url_request_context_adapter.cc
+++ b/components/cronet/android/url_request_context_adapter.cc
@@ -10,6 +10,7 @@
 #include "base/files/file_util.h"
 #include "base/files/scoped_file.h"
 #include "base/message_loop/message_loop.h"
+#include "base/prefs/pref_filter.h"
 #include "base/single_thread_task_runner.h"
 #include "components/cronet/url_request_context_config.h"
 #include "net/android/network_change_notifier_factory_android.h"
@@ -150,12 +151,28 @@ void URLRequestContextAdapter::InitRequestContextOnNetworkThread() {
   context_builder.set_proxy_config_service(proxy_config_service_.get());
   config_->ConfigureURLRequestContextBuilder(&context_builder);
 
+  // Set up pref file if storage path is specified.
+  if (!config_->storage_path.empty()) {
+    base::FilePath filepath(config_->storage_path);
+    filepath = filepath.Append(FILE_PATH_LITERAL("local_prefs_legacy.json"));
+    if (!file_thread_) {
+      file_thread_.reset(new base::Thread("Network File Thread"));
+      file_thread_->Start();
+    }
+    json_pref_store_ = new JsonPrefStore(filepath, file_thread_->task_runner(),
+                                         scoped_ptr<PrefFilter>());
+    json_pref_store_->ReadPrefsAsync(nullptr);
+    context_builder.SetFileTaskRunner(file_thread_->task_runner());
+  }
+
   context_.reset(context_builder.Build());
 
   if (config_->enable_sdch) {
     DCHECK(context_->sdch_manager());
     sdch_owner_.reset(
         new net::SdchOwner(context_->sdch_manager(), context_.get()));
+    if (json_pref_store_)
+      sdch_owner_->EnablePersistentStorage(json_pref_store_.get());
   }
 
   // Currently (circa M39) enabling QUIC requires setting probability threshold.