Never use CPU-built mips for Gray_8.

src/gpu/SkGr.cpp

 /*
  * Copyright 2010 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "SkGr.h"
 #include "SkGrPriv.h"
@@ skipping 331 matching lines @@
         if (texture) {
             return texture;
         }
     }
 
     sk_sp<GrTexture> texture(create_texture_from_yuv(ctx, bitmap, desc));
     if (texture) {
         return texture.release();
     }
 
+    // We don't support Gray8 directly in the GL backend, so fail-over to GrUploadBitmapToTexture.
+    // That will transform the Gray8 to 8888, then use the driver/GPU to build mipmaps. If we build
+    // the mips on the CPU here, they'll all be Gray8, which isn't useful. (They get treated as A8).
+    // TODO: A better option might be to transform the initial bitmap here to 8888, then run the
+    // CPU mip-mapper on that data before uploading. This is much less code for a rare case though:
+    if (kGray_8_SkColorType == bitmap.colorType()) {

[bsalomon, 2016/06/21 18:57:40]

Chris, I think we'll a similar failure mode for the deferred image texture data
code path.

+        return nullptr;
+    }
+
     SkASSERT(sizeof(int) <= sizeof(uint32_t));
     if (bitmap.width() < 0 || bitmap.height() < 0) {
         return nullptr;
     }
 
     SkAutoPixmapUnlock srcUnlocker;
     if (!bitmap.requestLock(&srcUnlocker)) {
         return nullptr;
     }
     const SkPixmap& pixmap = srcUnlocker.pixmap();
@@ skipping 411 matching lines @@
             SkErrorInternals::SetError( kInvalidPaint_SkError,
                                         "Sorry, I don't understand the filtering "
                                         "mode you asked for.  Falling back to "
                                         "MIPMaps.");
             textureFilterMode = GrTextureParams::kMipMap_FilterMode;
             break;
 
     }
     return textureFilterMode;
 }