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/GLProgramsTest.cpp b/tests/GLProgramsTest.cpp
index 2264385..899b42f 100644
--- a/tests/GLProgramsTest.cpp
+++ b/tests/GLProgramsTest.cpp
@@ -147,6 +147,10 @@
     dummyDesc.fHeight = 22;
     SkAutoTUnref<GrTexture> dummyTexture2(this->createTexture(dummyDesc, NULL, 0));
 
+    if (!dummyTexture1 || ! dummyTexture2) {
+        return false;
+    }
+
     static const int NUM_TESTS = 512;
 
     SkRandom random;