Use a single CGLContextObj to draw and update the IOSurface

content/browser/compositor/io_surface_context_mac.h

Index: content/browser/compositor/io_surface_context_mac.h
diff --git a/content/browser/compositor/io_surface_context_mac.h b/content/browser/compositor/io_surface_context_mac.h
index 2654711668b37028e1581a7fde60af4dc8d5ee62..04500e15dae94b59af891d75300f9deb9564c5b4 100644
--- a/content/browser/compositor/io_surface_context_mac.h
+++ b/content/browser/compositor/io_surface_context_mac.h
@@ -18,22 +18,16 @@
 
 namespace content {
 
+// The CGL context used to update and draw an IOSurface-backed texture. If an
+// error occurs on this context, or if the current GPU changes, then the
+// context is poisoned, and a new one is created.
 class IOSurfaceContext
     : public base::RefCounted<IOSurfaceContext>,
       public content::GpuDataManagerObserver {
  public:
-  enum Type {
-    // The number used to look up the context used for async readback and for
-    // initializing the IOSurface.
-    kOffscreenContext = -2,
-    // The number used to look up the context used by CAOpenGLLayers.
-    kCALayerContext = -3,
-  };
-
-  // Get or create a GL context of the specified type. Share these GL contexts
-  // as much as possible because creating and destroying them can be expensive.
-  // http://crbug.com/180463
-  static scoped_refptr<IOSurfaceContext> Get(Type type);
+  // Get or create a GL context. Share these GL contexts as much as possible
+  // because creating and destroying them can be expensive.
+  static scoped_refptr<IOSurfaceContext> Get();
 
   // Mark that all the GL contexts in the same sharegroup as this context as
   // invalid, so they shouldn't be returned anymore by Get, but rather, new
@@ -50,21 +44,14 @@ class IOSurfaceContext
  private:
   friend class base::RefCounted<IOSurfaceContext>;
 
-  IOSurfaceContext(
-      Type type,
-      base::ScopedTypeRef<CGLContextObj> clg_context_strong);
+  IOSurfaceContext(base::ScopedTypeRef<CGLContextObj> clg_context_strong);
   virtual ~IOSurfaceContext();
 
-  Type type_;
   base::ScopedTypeRef<CGLContextObj> cgl_context_;
-
   bool poisoned_;
 
-  // The global map from window number and window ordering to
-  // context data.
-  typedef std::map<Type, IOSurfaceContext*> TypeMap;
-  static base::LazyInstance<TypeMap> type_map_;
-  static TypeMap* type_map();
+  // The current non-poisoned context, shared by all layers.
+  static IOSurfaceContext* current_context_;
 };
 
 }  // namespace content