Support multiple null GL contexts on a thread.

samplecode/SampleApp.h

 /*
  * Copyright 2011 Skia
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SampleApp_DEFINED
 #define SampleApp_DEFINED
 
@@ skipping 20 matching lines @@
     SkTDArray<const SkViewFactory*> fSamples;
 public:
     enum DeviceType {
         kRaster_DeviceType,
         kPicture_DeviceType,
 #if SK_SUPPORT_GPU
         kGPU_DeviceType,
 #if SK_ANGLE
         kANGLE_DeviceType,
 #endif // SK_ANGLE
-        kNullGPU_DeviceType,
 #endif // SK_SUPPORT_GPU
 
         kDeviceTypeCnt
     };
 
     static bool IsGpuDeviceType(DeviceType devType) {
     #if SK_SUPPORT_GPU
         switch (devType) {
             case kGPU_DeviceType:
     #if SK_ANGLE
             case kANGLE_DeviceType:
     #endif // SK_ANGLE
-            case kNullGPU_DeviceType:
                 return true;
             default:
                 return false;
         }
     #endif // SK_SUPPORT_GPU
         return false;
     }
 
     /**
      * SampleApp ports can subclass this manager class if they want to:
@@ skipping 170 matching lines @@
     void installDrawFilter(SkCanvas*);
     int findByTitle(const char*);
     void listTitles();
     SkSize tileSize() const;
     bool sendAnimatePulse();
 
     typedef SkOSWindow INHERITED;
 };
 
 #endif