Lower the priority of environment and process data collection.

chrome/browser/safe_browsing/incident_reporting/environment_data_collection.cc

Index: chrome/browser/safe_browsing/incident_reporting/environment_data_collection.cc
diff --git a/chrome/browser/safe_browsing/incident_reporting/environment_data_collection.cc b/chrome/browser/safe_browsing/incident_reporting/environment_data_collection.cc
index f207502a3ac742370b8253646d1c654def211c02..56f6666a84578d0102e41a28b7a646e855b125ce 100644
--- a/chrome/browser/safe_browsing/incident_reporting/environment_data_collection.cc
+++ b/chrome/browser/safe_browsing/incident_reporting/environment_data_collection.cc
@@ -8,6 +8,8 @@
 
 #include "base/cpu.h"
 #include "base/sys_info.h"
+#include "base/threading/platform_thread.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "chrome/common/channel_info.h"
 #include "chrome/common/safe_browsing/csd.pb.h"
 #include "components/version_info/version_info.h"
@@ -62,6 +64,13 @@ void CollectProcessData(ClientIncidentReport_EnvironmentData_Process* process) {
 }  // namespace
 
 void CollectEnvironmentData(ClientIncidentReport_EnvironmentData* data) {
+  // Toggling priority only makes sense in a thread pool.
+  DCHECK(base::SequencedWorkerPool::GetWorkerPoolForCurrentThread());
+  // Lower priority for this task.
+  auto previous_priority = base::PlatformThread::GetCurrentThreadPriority();
+  base::PlatformThread::SetCurrentThreadPriority(
+      base::ThreadPriority::BACKGROUND);
+
   // OS
   {
     ClientIncidentReport_EnvironmentData_OS* os = data->mutable_os();
@@ -82,6 +91,9 @@ void CollectEnvironmentData(ClientIncidentReport_EnvironmentData* data) {
 
   // Process
   CollectProcessData(data->mutable_process());
+
+  // Reset the thread priority.
+  base::PlatformThread::SetCurrentThreadPriority(previous_priority);

[grt (UTC plus 2), 2015/12/14 21:10:25]

it would be hella bad if someone accidentally added a "return;" before this.
would you mind using base::ScopedClosureRunner up on line 73 to ensure that the
priority is always reverted? does this work:
  base::ScopedClosureRunner restore_priority(
      base::Bind(&base::PlatformThread::SetCurrentThreadPriority,
                 previous_priority));

[gab, 2015/12/15 16:49:38]

That sounds like a great idea to me, also keeps all priority related code at the
top :-). I felt like adding a new scoper for thread priority just for this CL
was overkill so I had refrained from asking but I didn't know about
ScopedClosureRunner :-), very useful for generic scopers!).

[proberge, 2015/12/16 15:19:38]

Done.

 }
 
 #if !defined(OS_WIN)