Fix alpha textures in NV ES3 contexts on Windows

tests/ImageNewShaderTest.cpp

Index: tests/ImageNewShaderTest.cpp
diff --git a/tests/ImageNewShaderTest.cpp b/tests/ImageNewShaderTest.cpp
index b4349e06331949638319bdb328d05e7ce7f9bb98..f34d066f6bbf590c557565547e29486c3c0dfa95 100644
--- a/tests/ImageNewShaderTest.cpp
+++ b/tests/ImageNewShaderTest.cpp
@@ -92,17 +92,29 @@ void rasterToGpu(skiatest::Reporter* reporter, GrContext* context) {
 }
 
 DEF_GPUTEST(ImageNewShader_GPU, reporter, factory) {
-    GrContext* context = factory->get(GrContextFactory::kNative_GLContextType);
+    for (int i= 0; i < GrContextFactory::kGLContextTypeCnt; ++i) {
+        GrContextFactory::GLContextType glCtxType = (GrContextFactory::GLContextType) i;
 
-    // GPU -> GPU
-    gpuToGpu(reporter, context);
+        if (!GrContextFactory::IsRenderingGLContext(glCtxType)) {
+            continue;
+        }
 
-    // GPU -> RASTER
-    gpuToRaster(reporter, context);
+        GrContext* context = factory->get(glCtxType);
 
+        if (NULL == context) {
+            continue;
+        }
 
-    // RASTER -> GPU
-    rasterToGpu(reporter, context);
+        // GPU -> GPU
+        gpuToGpu(reporter, context);
+
+        // GPU -> RASTER
+        gpuToRaster(reporter, context);
+
+
+        // RASTER -> GPU
+        rasterToGpu(reporter, context);
+    }
 }
 
 #endif