[Chromecast] Feature flag to disable idle socket close

Add new feature flag disable_idle_socket_close_on_memory_pressure. If
the flag is turned on, cast_shell won't close idle sockets when memory
pressure happens.

BUG=786585, internal b/73351220, internal b/73495670
TEST=Lauch cast_shell with enable-features=disable_... and watch logs

Change-Id: I5aa22a20103624c3114bc8de34412a9ace0dfa29
Reviewed-on: https://chromium-review.googlesource.com/922902Reviewed-by: Sergey Volk <servolk@chromium.org>
Commit-Queue: Yuchen Liu <yucliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537161}

chromecast/base/cast_features.cc

@@ -124,6 +124,11 @@ const base::Feature kTripleBuffer720{"enable_triple_buffer_720",
 // settings and takes precedence over triple-buffer feature).
 const base::Feature kSingleBuffer{"enable_single_buffer",
                                   base::FEATURE_DISABLED_BY_DEFAULT};
+// Disable idle sockets closing on memory pressure. See
+// chromecast/browser/url_request_context_factory.cc for usage.
+const base::Feature kDisableIdleSocketsCloseOnMemoryPressure{
+    "disable_idle_sockets_close_on_memory_pressure",
+    base::FEATURE_DISABLED_BY_DEFAULT};
 
 // End Chromecast Feature definitions.
 

chromecast/base/cast_features.h

@@ -25,6 +25,7 @@ extern const base::Feature kAllowUserMediaAccess;
 extern const base::Feature kEnableQuic;
 extern const base::Feature kTripleBuffer720;
 extern const base::Feature kSingleBuffer;
+extern const base::Feature kDisableIdleSocketsCloseOnMemoryPressure;
 
 // Below are utilities needed by the Cast receiver to persist feature
 // information. Client code which is simply querying the status of a feature

chromecast/browser/url_request_context_factory.cc

@@ -335,9 +335,17 @@ void URLRequestContextFactory::PopulateNetworkSessionParams(
   LOG(INFO) << "Set HttpNetworkSessionParams.enable_quic = "
             << session_params->enable_quic;
 
-  // Do not close idle sockets on memory pressure, otherwise it will open too
-  // much connections to the server.
-  session_params->disable_idle_sockets_close_on_memory_pressure = true;
+  // Disable idle sockets close on memory pressure, if instructed by DCS. On
+  // memory constrained devices:
+  // 1. if idle sockets are closed when memory pressure happens, cast_shell will
+  // close and re-open lots of connections to server.
+  // 2. if idle sockets are kept alive when memory pressure happens, this may
+  // cause JS engine gc frequently, leading to JS suspending.
+  session_params->disable_idle_sockets_close_on_memory_pressure =
+      base::FeatureList::IsEnabled(kDisableIdleSocketsCloseOnMemoryPressure);
+  LOG(INFO) << "Set HttpNetworkSessionParams."
+            << "disable_idle_sockets_close_on_memory_pressure = "
+            << session_params->disable_idle_sockets_close_on_memory_pressure;
 }
 
 net::URLRequestContext* URLRequestContextFactory::CreateSystemRequestContext() {