Add plot-based purging to GrLayerCache

src/gpu/GrAtlas.h

Index: src/gpu/GrAtlas.h
diff --git a/src/gpu/GrAtlas.h b/src/gpu/GrAtlas.h
index 9ccbc53bc605331dcab16725f6658862eb870f3d..1e91d1e90ee111833cf0c3a83fe0c71e4960dce3 100644
--- a/src/gpu/GrAtlas.h
+++ b/src/gpu/GrAtlas.h
@@ -81,6 +81,12 @@ public:
     public:
         bool isEmpty() const { return 0 == fPlots.count(); }
 
+#ifdef SK_DEBUG
+        bool contains(const GrPlot* plot) const { 
+            return fPlots.contains(const_cast<GrPlot*>(plot)); 
+        }
+#endif
+
     private:
         SkTDArray<GrPlot*> fPlots;
 
@@ -112,6 +118,18 @@ public:
 
     void uploadPlotsToTexture();
 
+    enum IterOrder {
+        kLRUFirst_IterOrder,
+        kMRUFirst_IterOrder
+    };
+
+    typedef GrPlotList::Iter PlotIter;
+    GrPlot* iterInit(PlotIter* iter, IterOrder order) {
+        return iter->init(fPlotList, kLRUFirst_IterOrder == order 
+                                                       ? GrPlotList::Iter::kTail_IterStart
+                                                       : GrPlotList::Iter::kHead_IterStart);
+    }
+
 private:
     void makeMRU(GrPlot* plot);