Never use CPU-built mips for Gray_8.

src/gpu/SkGr.cpp

Index: src/gpu/SkGr.cpp
diff --git a/src/gpu/SkGr.cpp b/src/gpu/SkGr.cpp
index f937b16d55e166f0d1481186752e4507a2ed4816..1e4ff527520e6e680cae0df80d5dc976878e9a6e 100644
--- a/src/gpu/SkGr.cpp
+++ b/src/gpu/SkGr.cpp
@@ -349,6 +349,15 @@ GrTexture* GrGenerateMipMapsAndUploadToTexture(GrContext* ctx, const SkBitmap& b
         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;