Bug 1473732 - Base default number of OMTP workers on the number of logical CPU cores. r=rhunt

system-info is a stub on Tier3 platforms while physical vs. logical
difference only matters for hyper-threading. As hyper-threading
is usually available on CPUs with more than 2 physical cores this
change has no impact there as the default is clamped to [1, 4].
However, on Intel i3-* CPUs with 2 physical and 4 logical cores this
bumps the default from 1 to 3.

MozReview-Commit-ID: 1Yh8rJL2JcN

--HG--
extra : rebase_source : 77613cbb99c14f19217592080bfd51ea2194422b

gfx/layers/PaintThread.cpp

@@ -22,7 +22,7 @@
 #include "mozilla/SyncRunnable.h"
 #include "nsIPropertyBag2.h"
 #include "nsServiceManagerUtils.h"
-#include "nsSystemInfo.h"
+#include "prsystem.h"
 
 // Uncomment the following line to dispatch sync runnables when
 // painting so that rasterization happens synchronously from
@@ -156,15 +156,7 @@ PaintThread::AddRef()
 /* static */ int32_t
 PaintThread::CalculatePaintWorkerCount()
 {
-  int32_t cpuCores = 1;
-  nsCOMPtr<nsIPropertyBag2> systemInfo = do_GetService(NS_SYSTEMINFO_CONTRACTID);
-  if (systemInfo) {
-    nsresult rv = systemInfo->GetPropertyAsInt32(NS_LITERAL_STRING("cpucores"), &cpuCores);
-    if (NS_FAILED(rv)) {
-      cpuCores = 1;
-    }
-  }
-
+  int32_t cpuCores = PR_GetNumberOfProcessors();
   int32_t workerCount = gfxPrefs::LayersOMTPPaintWorkers();
 
   // If not manually specified, default to (cpuCores * 3) / 4, and clamp