Add a makeDrawContextWithFallback that handles config fallback

include/gpu/GrContext.h

 /*
  * Copyright 2010 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrContext_DEFINED
 #define GrContext_DEFINED
 
@@ skipping 176 matching lines @@
      */
     sk_sp<GrDrawContext> makeDrawContext(SkBackingFit fit, 
                                          int width, int height,
                                          GrPixelConfig config,
                                          sk_sp<SkColorSpace> colorSpace,
                                          int sampleCnt = 0,
                                          GrSurfaceOrigin origin = kDefault_GrSurfaceOrigin,
                                          const SkSurfaceProps* surfaceProps = nullptr,
                                          SkBudgeted = SkBudgeted::kYes);
 
+    /*
+     * This method will attempt to create a drawContext that has, at least, the number of
+     * channels and precision per channel as requested in 'config' (e.g., A8 and 888 can be
+     * converted to 8888). It may also swizzle the channels (e.g., BGRA -> RGBA).
+     * SRGB-ness will be preserved.
+     */
+    sk_sp<GrDrawContext> makeDrawContextWithFallback(
+                                                 SkBackingFit fit,
+                                                 int width, int height,
+                                                 GrPixelConfig config,
+                                                 sk_sp<SkColorSpace> colorSpace,
+                                                 int sampleCnt = 0,
+                                                 GrSurfaceOrigin origin = kDefault_GrSurfaceOrigin,
+                                                 const SkSurfaceProps* surfaceProps = nullptr,
+                                                 SkBudgeted budgeted = SkBudgeted::kYes);
+
     ///////////////////////////////////////////////////////////////////////////
     // Misc.
 
     /**
      * Flags that affect flush() behavior.
      */
     enum FlushBits {
         /**
          * A client may reach a point where it has partially rendered a frame
          * through a GrContext that it knows the user will never see. This flag
@@ skipping 276 matching lines @@
     SkAutoTUnref<const GrCaps>  fCaps;
     uint32_t                    fContextUniqueID;
 
     friend class GrContext;
     friend class SkImage;
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif