Convert GrPorterDuff test from NullGL to Mock context

Bug: skia:
Change-Id: Id403aabcae1dbf38e55381bb3b4353e85a12a745
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/203705
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>

include/gpu/mock/GrMockTypes.h

@@ -68,6 +68,7 @@ struct GrMockOptions {
     int fMaxVertexSamplers = 0;
     int fMaxFragmentSamplers = 8;
     bool fShaderDerivativeSupport = true;
+    bool fDualSourceBlendingSupport = false;
 
     // GrMockGpu options.
     bool fFailTextureAllocations = false;

src/gpu/mock/GrMockCaps.h

@@ -31,6 +31,7 @@ class GrMockCaps : public GrCaps {
         fShaderCaps->fFlatInterpolationSupport = options.fFlatInterpolationSupport;
         fShaderCaps->fMaxFragmentSamplers = options.fMaxFragmentSamplers;
         fShaderCaps->fShaderDerivativeSupport = options.fShaderDerivativeSupport;
+        fShaderCaps->fDualSourceBlendingSupport = options.fDualSourceBlendingSupport;
 
         this->applyOptionsOverrides(contextOptions);
     }

tests/GrPorterDuffTest.cpp

@@ -27,8 +27,12 @@ static void test_color_opaque_no_coverage(skiatest::Reporter* reporter, const Gr
 static void test_lcd_coverage(skiatest::Reporter* reporter, const GrCaps& caps);
 static void test_lcd_coverage_fallback_case(skiatest::Reporter* reporter, const GrCaps& caps);
 
-DEF_GPUTEST_FOR_NULLGL_CONTEXT(GrPorterDuff, reporter, ctxInfo) {
-    const GrCaps& caps = *ctxInfo.grContext()->priv().getGpu()->caps();
+DEF_GPUTEST(GrPorterDuff, reporter, /*ctxInfo*/) {
+    GrMockOptions mockOptions;
+    mockOptions.fDualSourceBlendingSupport = true;
+    auto context = GrContext::MakeMock(&mockOptions, GrContextOptions());
+    const GrCaps& caps = *context->priv().getGpu()->caps();
+
     if (!caps.shaderCaps()->dualSourceBlendingSupport()) {
         SK_ABORT("Null context does not support dual source blending.");
         return;