bump the size of the atlas id to 64 bits

src/gpu/GrBatchAtlas.h

Index: src/gpu/GrBatchAtlas.h
diff --git a/src/gpu/GrBatchAtlas.h b/src/gpu/GrBatchAtlas.h
index 83ef5ec732e345eafa5b2bb91d0700fc7038823a..ce3e40aec4830a3a1deb3827ef3b17ac231d2249 100644
--- a/src/gpu/GrBatchAtlas.h
+++ b/src/gpu/GrBatchAtlas.h
@@ -24,7 +24,7 @@ public:
     typedef uint64_t BatchToken;
     // An AtlasID is an opaque handle which callers can use to determine if the atlas contains
     // a specific piece of data
-    typedef uint32_t AtlasID;
+    typedef uint64_t AtlasID;
     static const uint32_t kInvalidAtlasID = 0;
     static const uint64_t kInvalidAtlasGeneration = 0;
 
@@ -107,12 +107,13 @@ public:
     }
 
 private:
-    static int GetIndexFromID(AtlasID id) {
+    static uint32_t GetIndexFromID(AtlasID id) {
         return id & 0xffff;
     }
 
-    static int GetGenerationFromID(AtlasID id) {
-        return (id >> 16) & 0xffff;
+    // top 48 bits are reserved for the generation ID
+    static uint64_t GetGenerationFromID(AtlasID id) {
+        return (id >> 16) & 0xffffffffffff;
     }
 
     inline void updatePlot(GrBatchTarget*, AtlasID*, BatchPlot*);
@@ -122,10 +123,10 @@ private:
     inline void processEviction(AtlasID);
 
     GrTexture* fTexture;
-    int fNumPlotsX;
-    int fNumPlotsY;
-    int fPlotWidth;
-    int fPlotHeight;
+    uint32_t fNumPlotsX;
+    uint32_t fNumPlotsY;
+    uint32_t fPlotWidth;
+    uint32_t fPlotHeight;
     size_t fBPP;
     uint64_t fAtlasGeneration;