Add config options to run different GPU APIs to dm and nanobench

dm/DMSrcSink.h

Index: dm/DMSrcSink.h
diff --git a/dm/DMSrcSink.h b/dm/DMSrcSink.h
index 63d6717e78c299bfb35f2d969d7742e67a84e7b5..5e053b1155cfd57106bbc96e665bb53c8d3d720a 100644
--- a/dm/DMSrcSink.h
+++ b/dm/DMSrcSink.h
@@ -214,10 +214,8 @@ public:
 
 class GPUSink : public Sink {
 public:
-    GPUSink(GrContextFactory::GLContextType, GrGLStandard, int samples,
-            bool diText, bool threaded);
     GPUSink(GrContextFactory::GLContextType, GrContextFactory::GLContextOptions,
-            GrGLStandard, int samples, bool diText, bool threaded);
+            int samples, bool diText, bool threaded);
 
     Error draw(const Src&, SkBitmap*, SkWStream*, SkString*) const override;
     int enclave() const override;
@@ -226,7 +224,6 @@ public:
 private:
     GrContextFactory::GLContextType    fContextType;
     GrContextFactory::GLContextOptions fContextOptions;
-    GrGLStandard                       fGpuAPI;
     int                                fSampleCount;
     bool                               fUseDIText;
     bool                               fThreaded;