Fix alpha textures in NV ES3 contexts on Windows.

Make unit tests iterate over all the rendering GL context types rather than using kNative.

Fix the extension printing when gStartupSpew is set.

R=jvanverth@google.com

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/398183002
diff --git a/tests/ImageNewShaderTest.cpp b/tests/ImageNewShaderTest.cpp
index b4349e0..f34d066 100644
--- a/tests/ImageNewShaderTest.cpp
+++ b/tests/ImageNewShaderTest.cpp
@@ -92,17 +92,29 @@
 }
 
 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;
+        }
+
+        // GPU -> GPU
+        gpuToGpu(reporter, context);
+
+        // GPU -> RASTER
+        gpuToRaster(reporter, context);
 
 
-    // RASTER -> GPU
-    rasterToGpu(reporter, context);
+        // RASTER -> GPU
+        rasterToGpu(reporter, context);
+    }
 }
 
 #endif