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

src/gpu/SkGpuDevice.cpp

Index: src/gpu/SkGpuDevice.cpp
diff --git a/src/gpu/SkGpuDevice.cpp b/src/gpu/SkGpuDevice.cpp
index b719f84278d35dca18398d756aef313531c9527e..0ec2b858c43c23bbaab8ee7741345c3c33e096df 100644
--- a/src/gpu/SkGpuDevice.cpp
+++ b/src/gpu/SkGpuDevice.cpp
@@ -1765,9 +1765,9 @@ bool SkGpuDevice::filterTextFlags(const SkPaint& paint, TextFlags* flags) {
         paint.getPathEffect() ||
         paint.isFakeBoldText() ||
         paint.getStyle() != SkPaint::kFill_Style) {
-        // 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