Add alpha type to texture producer

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2250403003

Review-Url: https://codereview.chromium.org/2250403003
diff --git a/src/gpu/GrImageIDTextureAdjuster.cpp b/src/gpu/GrImageIDTextureAdjuster.cpp
index f9aaae1..5a96b6d 100644
--- a/src/gpu/GrImageIDTextureAdjuster.cpp
+++ b/src/gpu/GrImageIDTextureAdjuster.cpp
@@ -62,6 +62,10 @@
     GrInstallBitmapUniqueKeyInvalidator(copyKey, fBitmap.pixelRef());
 }
 
+SkAlphaType GrBitmapTextureMaker::alphaType() const {
+    return fBitmap.alphaType();
+}
+
 SkColorSpace* GrBitmapTextureMaker::getColorSpace() {
     return fBitmap.colorSpace();
 }
@@ -101,6 +105,10 @@
     }
 }
 
+SkAlphaType GrImageTextureMaker::alphaType() const {
+    return fCacher->info().alphaType();
+}
+
 SkColorSpace* GrImageTextureMaker::getColorSpace() {
     return fCacher->info().colorSpace();
 }