when we disable lcd for impl reasons, add kGenA8 to document the original intent

src/core/SkBitmapDevice.cpp

Index: src/core/SkBitmapDevice.cpp
diff --git a/src/core/SkBitmapDevice.cpp b/src/core/SkBitmapDevice.cpp
index 2711004aef14de4fbda9fbe12f2c74b171acdfa5..3af47f6e9637d1cd2a24ca8bfe3fd91c34cba848 100644
--- a/src/core/SkBitmapDevice.cpp
+++ b/src/core/SkBitmapDevice.cpp
@@ -386,9 +386,9 @@ bool SkBitmapDevice::filterTextFlags(const SkPaint& paint, TextFlags* flags) {
         paint.isFakeBoldText() ||
         paint.getStyle() != SkPaint::kFill_Style ||
         !SkXfermode::IsMode(paint.getXfermode(), SkXfermode::kSrcOver_Mode)) {
-        // turn off lcd
+        // turn off lcd, but turn on kGenA8
         flags->fFlags = paint.getFlags() & ~SkPaint::kLCDRenderText_Flag;
-        flags->fHinting = paint.getHinting();
+        flags->fFlags |= SkPaint::kGenA8FromLCD_Flag;
         return true;
     }
     // we're cool with the paint as is