Rename GrContextFactory::ContextOptions to ContextOverrides

Also changes the behavior of these flags to only override their             
corresponding context options when set, and to leave them unchanged    
when not set.  

BUG=skia:

Change-Id: I09f6be09997594fa888d9045dd4901354ef3f880
Reviewed-on: https://skia-review.googlesource.com/8780
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
diff --git a/dm/DMGpuSupport.h b/dm/DMGpuSupport.h
index 1ea51d2..75bfc3b 100644
--- a/dm/DMGpuSupport.h
+++ b/dm/DMGpuSupport.h
@@ -31,13 +31,13 @@
 static inline sk_sp<SkSurface> NewGpuSurface(
         sk_gpu_test::GrContextFactory* grFactory,
         sk_gpu_test::GrContextFactory::ContextType type,
-        sk_gpu_test::GrContextFactory::ContextOptions options,
+        sk_gpu_test::GrContextFactory::ContextOverrides overrides,
         SkImageInfo info,
         int samples,
         bool useDIText) {
     uint32_t flags = useDIText ? SkSurfaceProps::kUseDeviceIndependentFonts_Flag : 0;
     SkSurfaceProps props(flags, SkSurfaceProps::kLegacyFontHost_InitType);
-    return SkSurface::MakeRenderTarget(grFactory->get(type, options), SkBudgeted::kNo,
+    return SkSurface::MakeRenderTarget(grFactory->get(type, overrides), SkBudgeted::kNo,
                                        info, samples, &props);
 }
 
@@ -63,7 +63,7 @@
 namespace sk_gpu_test {
 class GrContextFactory {
 public:
-    GrContextFactory() {};
+    GrContextFactory() {}
     explicit GrContextFactory(const GrContextOptions&) {}
 
     typedef int ContextType;
@@ -80,10 +80,7 @@
                              kNullGL_ContextType        = 0,
                              kVulkan_ContextType        = 0;
     static const int kContextTypeCnt = 1;
-    enum ContextOptions {
-        kNone_ContextOptions = 0,
-        kEnableNVPR_ContextOptions = 0x1,
-    };
+    enum class ContextOverrides {};
     void destroyContexts() {}
 
     void abandonContexts() {}
@@ -98,7 +95,7 @@
 
 static inline SkSurface* NewGpuSurface(sk_gpu_test::GrContextFactory*,
                                        sk_gpu_test::GrContextFactory::ContextType,
-                                       sk_gpu_test::GrContextFactory::ContextOptions,
+                                       sk_gpu_test::GrContextFactory::ContextOverrides,
                                        SkImageInfo,
                                        int,
                                        bool) {