Implement support for KHR_blend_equation_advanced

include/gpu/GrProcessorUnitTest.h

Index: include/gpu/GrProcessorUnitTest.h
diff --git a/include/gpu/GrProcessorUnitTest.h b/include/gpu/GrProcessorUnitTest.h
index 4b97483c0fa438f017c2c6728ed04c2b5084bd44..f417c7dd94dfbf130506fda0b6365efee4658cc8 100644
--- a/include/gpu/GrProcessorUnitTest.h
+++ b/include/gpu/GrProcessorUnitTest.h
@@ -115,10 +115,21 @@ public:
                                   const GrDrawTargetCaps& caps,
                                   GrTexture* dummyTextures[]) {
         VerifyFactoryCount();
-        SkASSERT(GetFactories()->count());
-        uint32_t idx = random->nextRangeU(0, GetFactories()->count() - 1);
-        GrProcessorTestFactory<Processor>* factory = (*GetFactories())[idx];
-        return factory->fCreateProc(random, context, caps, dummyTextures);
+        int count = GetFactories()->count();
+        SkASSERT(count);
+        uint32_t idx = random->nextRangeU(0, count - 1);
+        Processor* p = (*GetFactories())[idx]->fCreateProc(random, context, caps, dummyTextures);
+        if (!p) {
+            // Factory at idx was not supported on this GrContext. Find one that is.
+            SkSTArray<8, GrProcessorTestFactory<Processor>*, true> localFactories(*GetFactories());
+            do {
+                count--;
+                SkASSERT(count);
+                SkTSwap(localFactories[idx], localFactories[count]);
+                idx = random->nextRangeU(0, count - 1);
+            } while (!(p = localFactories[idx]->fCreateProc(random, context, caps, dummyTextures)));
+        }
+        return p;
     }
 
     /*