[Cronet] Enable persistence mode for Sdch

components/cronet/android/cronet_url_request_context_adapter.cc

Index: components/cronet/android/cronet_url_request_context_adapter.cc
diff --git a/components/cronet/android/cronet_url_request_context_adapter.cc b/components/cronet/android/cronet_url_request_context_adapter.cc
index ec52c9a4c1721a4219f836f1ef40024629276dd0..f71f10ca55c3995465b775a1d742ea1c0e51588c 100644
--- a/components/cronet/android/cronet_url_request_context_adapter.cc
+++ b/components/cronet/android/cronet_url_request_context_adapter.cc
@@ -10,6 +10,7 @@
 #include "base/files/file_util.h"
 #include "base/files/scoped_file.h"
 #include "base/logging.h"
+#include "base/prefs/pref_filter.h"
 #include "base/single_thread_task_runner.h"
 #include "base/values.h"
 #include "components/cronet/url_request_context_config.h"
@@ -103,6 +104,12 @@ class BasicNetworkDelegate : public net::NetworkDelegateImpl {
   DISALLOW_COPY_AND_ASSIGN(BasicNetworkDelegate);
 };
 
+void CreatePrefFileIfNeeded(base::FilePath filepath) {
+  if (base::PathExists(filepath))
+    return;
+  base::WriteFile(filepath, "{}", 2);

[mmenke, 2015/05/11 17:16:19]

Is this really needed?  I don't see any documentation on the subject.  Also, I
don't see any other consumers doing this.

[xunjieli, 2015/05/12 19:17:50]

Done. Thanks! I saw an error from json pref store complaining about no file
found, so I added this part. It turns out that error isn't critical, and a new
file is created anyway. I will remove this part.

+}
+
 }  // namespace
 
 namespace cronet {
@@ -155,6 +162,23 @@ void CronetURLRequestContextAdapter::InitializeOnNetworkThread(
   context_builder.set_proxy_config_service(proxy_config_service_.release());
   config->ConfigureURLRequestContextBuilder(&context_builder);
 
+  // Only set up pref file if http disk cache is enabled.

[mef, 2015/05/12 16:39:17]

I think we should set pref file if storage_path is specified, regardless of http
cache settings.

[xunjieli, 2015/05/12 19:17:49]

Done.

+  if (!config->storage_path.empty() && !config->load_disable_cache) {
+    base::FilePath filepath(config->storage_path);
+    filepath = filepath.Append(FILE_PATH_LITERAL("local_prefs.json"));
+    if (!file_thread_) {
+      file_thread_.reset(new base::Thread("Network File Thread"));
+      file_thread_->StartWithOptions(
+          base::Thread::Options(base::MessageLoop::TYPE_DEFAULT, 0));
+    }
+    file_thread_->task_runner()->PostTask(
+        FROM_HERE, base::Bind(&CreatePrefFileIfNeeded, filepath));
+    network_json_store_ = new JsonPrefStore(
+        filepath, file_thread_->task_runner(), scoped_ptr<PrefFilter>());
+    network_json_store_->ReadPrefsAsync(nullptr);

[mef, 2015/05/12 16:39:17]

It seems that prefstore should just fallback to empty prefs on non-existent
file:
https://code.google.com/p/chromium/codesearch#chromium/src/base/prefs/json_pr...

[xunjieli, 2015/05/12 19:17:50]

Done. Yes, you and Matt are both right about this part. Somehow I thought the
error was critical when I saw the print statement in the logs.

+    context_builder.SetFileTaskRunner(file_thread_->task_runner());
+  }
+
   context_.reset(context_builder.Build());
 
   default_load_flags_ = net::LOAD_DO_NOT_SAVE_COOKIES |
@@ -166,6 +190,8 @@ void CronetURLRequestContextAdapter::InitializeOnNetworkThread(
     DCHECK(context_->sdch_manager());
     sdch_owner_.reset(
         new net::SdchOwner(context_->sdch_manager(), context_.get()));
+    if (network_json_store_)
+      sdch_owner_->EnablePersistentStorage(network_json_store_.get());
   }
 
   // Currently (circa M39) enabling QUIC requires setting probability threshold.