Support using OpenGL ES context on desktop

Support using OpenGL ES context on desktop for unix and Android platforms. This
is mainly useful in development.

Add --gpuAPI flag to gm, dm, bench, bench_pictures and render_pictures. The
possible parameters for the flag are "gl" and "gles".

R=bsalomon@google.com, mtklein@google.com, robertphillips@google.com

Author: kkinnunen@nvidia.com

Review URL: https://codereview.chromium.org/319043005
diff --git a/experimental/PdfViewer/pdf_viewer_main.cpp b/experimental/PdfViewer/pdf_viewer_main.cpp
index 2f1a055..c1b0284 100644
--- a/experimental/PdfViewer/pdf_viewer_main.cpp
+++ b/experimental/PdfViewer/pdf_viewer_main.cpp
@@ -168,7 +168,8 @@
 #if SK_SUPPORT_GPU
         else if (strcmp(FLAGS_config[0], "gpu") == 0) {
             SkAutoTUnref<GrSurface> target;
-            GrContext* gr = gContextFactory.get(GrContextFactory::kNative_GLContextType);
+            GrContext* gr = gContextFactory.get(GrContextFactory::kNative_GLContextType,
+                                                kNone_GrGLStandard);
             if (gr) {
                 // create a render target to back the device
                 GrTextureDesc desc;