Cherry pick fix for skbug.com/5734 to M54

src/effects/SkBlurMaskFilter.cpp

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBlurMaskFilter.h"
 #include "SkBlurMask.h"
 #include "SkGpuBlurUtils.h"
@@ skipping 1102 matching lines @@
     for (auto c : { SkRRect::kUpperLeft_Corner,  SkRRect::kUpperRight_Corner,
                     SkRRect::kLowerRight_Corner, SkRRect::kLowerLeft_Corner }) {
         SkASSERT(SkScalarIsInt(rrectToDraw.radii(c).fX) && SkScalarIsInt(rrectToDraw.radii(c).fY));
         builder[index++] = SkScalarCeilToInt(rrectToDraw.radii(c).fX);
         builder[index++] = SkScalarCeilToInt(rrectToDraw.radii(c).fY);
     }
     builder.finish();
 
     sk_sp<GrTexture> mask(context->textureProvider()->findAndRefTextureByUniqueKey(key));
     if (!mask) {
+        GrPixelConfig config;
+        if (context->caps()->isConfigRenderable(kAlpha_8_GrPixelConfig, false)) {
+            config = kAlpha_8_GrPixelConfig;
+        } else {
+            config = kRGBA_8888_GrPixelConfig;
+        }
+
         // TODO: this could be approx but the texture coords will need to be updated
         sk_sp<GrDrawContext> dc(context->makeDrawContext(SkBackingFit::kExact,
                                                          size.fWidth, size.fHeight,
-                                                         kAlpha_8_GrPixelConfig, nullptr));
+                                                         config, nullptr));
         if (!dc) {
             return nullptr;
         }
                 
         GrPaint grPaint;
         grPaint.setAntiAlias(doAA);
 
         dc->clear(nullptr, 0x0, true);
         dc->drawRRect(GrNoClip(), grPaint, SkMatrix::I(), rrectToDraw, GrStyle::SimpleFill());
 
@@ skipping 425 matching lines @@
     } else {
         str->append("None");
     }
     str->append("))");
 }
 #endif
 
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(SkBlurMaskFilter)
     SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkBlurMaskFilterImpl)
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END