Bug 982141 - Factor out 'wantSubAPZC' into nsLayoutUtils. r=kats,tn

--HG--
extra : rebase_source : c23e9d3253991523f39d7437ab5f36172768813a

layout/base/nsLayoutUtils.cpp

@@ -41,6 +41,7 @@
 #include "nsIWidget.h"
 #include "gfxMatrix.h"
 #include "gfxPoint3D.h"
+#include "gfxPrefs.h"
 #include "gfxTypes.h"
 #include "nsTArray.h"
 #include "mozilla/dom/HTMLCanvasElement.h"
@@ -6402,6 +6403,19 @@ nsLayoutUtils::CalculateExpandedScrollableRect(nsIFrame* aFrame)
   return scrollableRect;
 }
 
+/* static */ bool
+nsLayoutUtils::WantSubAPZC()
+{
+   // TODO Turn this on for inprocess OMTC on all platforms
+   bool wantSubAPZC = gfxPrefs::APZSubframeEnabled();
+#ifdef MOZ_WIDGET_GONK
+   if (XRE_GetProcessType() != GeckoProcessType_Content) {
+     wantSubAPZC = false;
+   }
+#endif
+   return wantSubAPZC;
+ }
+
 nsLayoutUtils::SurfaceFromElementResult::SurfaceFromElementResult()
   // Use safe default values here
   : mIsWriteOnly(true), mIsStillLoading(false), mCORSUsed(false)

layout/base/nsLayoutUtils.h

@@ -2133,6 +2133,12 @@ public:
   static nsRect
   CalculateExpandedScrollableRect(nsIFrame* aFrame);
 
+  /**
+   * Return whether we want to use APZ for subframes in this process.
+   * Currently we don't support APZ for the parent process on B2G.
+   */
+  static bool WantSubAPZC();
+
 private:
   static uint32_t sFontSizeInflationEmPerLine;
   static uint32_t sFontSizeInflationMinTwips;

layout/generic/nsGfxScrollFrame.cpp

@@ -2595,15 +2595,8 @@ ScrollFrameHelper::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
   if (mShouldBuildScrollableLayer) {
     shouldBuildLayer = true;
   } else {
-    // TODO Turn this on for inprocess OMTC on all platforms
-    bool wantSubAPZC = gfxPrefs::APZSubframeEnabled();
-#ifdef MOZ_WIDGET_GONK
-    if (XRE_GetProcessType() != GeckoProcessType_Content) {
-      wantSubAPZC = false;
-    }
-#endif
     shouldBuildLayer =
-      wantSubAPZC &&
+      nsLayoutUtils::WantSubAPZC() &&
       WantAsyncScroll() &&
       // If we are the root scroll frame for the display root then we don't need a scroll
       // info layer to make a RecordFrameMetrics call for us as