Flapper field trial to use workerpool for sync file operations.

content/browser/renderer_host/pepper/pepper_file_message_filter.cc

Index: content/browser/renderer_host/pepper/pepper_file_message_filter.cc
diff --git a/content/browser/renderer_host/pepper/pepper_file_message_filter.cc b/content/browser/renderer_host/pepper/pepper_file_message_filter.cc
index 5de7fbf19fcda606694d66f38d7f78e7f1cf80e5..e07bb990a01974cab3aa72a76a4b58b9386e0b33 100644
--- a/content/browser/renderer_host/pepper/pepper_file_message_filter.cc
+++ b/content/browser/renderer_host/pepper/pepper_file_message_filter.cc
@@ -8,8 +8,10 @@
 #include "base/file_path.h"
 #include "base/file_util.h"
 #include "base/logging.h"
+#include "base/metrics/field_trial.h"
 #include "base/platform_file.h"
 #include "base/process_util.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "content/browser/child_process_security_policy_impl.h"
 #include "content/browser/renderer_host/render_process_host_impl.h"
 #include "content/public/browser/browser_thread.h"
@@ -60,20 +62,67 @@ IPC::PlatformFileForTransit PlatformFileToPlatformFileForTransit(
   return file;
 }
 
+// Run a field trial comparing the effect of the FILE thread versus
+// blocking worker pool on hung-plugin reports.
+// TODO(shess): Remove once the workpool is proven superior.
+// http://crbug.com/153383
+const char* const kIOFieldTrialName = "FlapperIOThread";
+const char* const kPoolGroupName = "PoolThread";
+const char* const kFileGroupName = "FileThread";
+
+bool g_use_file_thread = true;
+
+void ActivateThreadFieldTrial() {
+  static bool activated = false;
+  if (activated)
+    return;
+
+  activated = true;
+
+  // The field trial will expire on Jan 1st, 2014.
+  scoped_refptr<base::FieldTrial> trial(
+      base::FieldTrialList::FactoryGetFieldTrial(
+          kIOFieldTrialName, 1000, kPoolGroupName, 2014, 1, 1, NULL));
+
+  // 50% goes into the FILE thread group.
+  trial->AppendGroup(kFileGroupName, 500);
+
+  g_use_file_thread = (trial->group_name() == kFileGroupName);
+}
+
 }  // namespace
 
 PepperFileMessageFilter::PepperFileMessageFilter(int child_id)
         : child_id_(child_id),
           channel_(NULL) {
+  ActivateThreadFieldTrial();
 }
 
 void PepperFileMessageFilter::OverrideThreadForMessage(
     const IPC::Message& message,
     BrowserThread::ID* thread) {
-  if (IPC_MESSAGE_CLASS(message) == PepperFileMsgStart)
+  if (IPC_MESSAGE_CLASS(message) == PepperFileMsgStart && g_use_file_thread)
     *thread = BrowserThread::FILE;
 }
 
+base::TaskRunner* PepperFileMessageFilter::OverrideTaskRunnerForMessage(
+    const IPC::Message& message) {
+  // The blocking pool provides a pool of threads to run file
+  // operations, instead of a single thread which might require
+  // queuing time.  Since these messages are synchronous as sent from
+  // the plugin, the sending thread cannot send a new message until
+  // this one returns, so there is no need to sequence tasks here.  If
+  // the plugin has multiple threads, it cannot make assumptions about
+  // ordering of IPC message sends, so it cannot make assumptions
+  // about ordering of operations caused by those IPC messages.
+  if (IPC_MESSAGE_CLASS(message) == PepperFileMsgStart) {
+    // Should never get here if using the FILE thread.
+    DCHECK(!g_use_file_thread);
+    return BrowserThread::GetBlockingPool();
+  }
+  return NULL;
+}
+
 bool PepperFileMessageFilter::OnMessageReceived(const IPC::Message& message,
                                                 bool* message_was_ok) {
   bool handled = true;