Include scaler context flags (gamma and contrast boost) in the text blob cache key.

src/gpu/text/GrAtlasTextBlob.h

Index: src/gpu/text/GrAtlasTextBlob.h
diff --git a/src/gpu/text/GrAtlasTextBlob.h b/src/gpu/text/GrAtlasTextBlob.h
index 3fd45990eb55bf225c288859ff9734c90c41b4a2..084de620c320409fe185599412d2ed60934760f9 100644
--- a/src/gpu/text/GrAtlasTextBlob.h
+++ b/src/gpu/text/GrAtlasTextBlob.h
@@ -61,6 +61,7 @@ public:
         SkPaint::Style fStyle;
         SkPixelGeometry fPixelGeometry;
         bool fHasBlur;
+        uint32_t fScalerContextFlags;
 
         bool operator==(const Key& other) const {
             return 0 == memcmp(this, &other, sizeof(Key));