Allow decoding JPEG into A8.

src/images/SkImageDecoder_libjpeg.cpp

Index: src/images/SkImageDecoder_libjpeg.cpp
diff --git a/src/images/SkImageDecoder_libjpeg.cpp b/src/images/SkImageDecoder_libjpeg.cpp
index bea1e98641f65725d1087576f9b191c820ec9f3f..e4d7ace0d48295d32c98ba4805909a2204e69afc 100644
--- a/src/images/SkImageDecoder_libjpeg.cpp
+++ b/src/images/SkImageDecoder_libjpeg.cpp
@@ -289,21 +289,33 @@ bool SkJPEGImageDecoder::onDecode(SkStream* stream, SkBitmap* bm, Mode mode) {
     /* this gives another few percents */
     cinfo.do_block_smoothing = 0;
 
+    SrcDepth srcDepth = k32Bit_SrcDepth;
     /* default format is RGB */
     if (cinfo.jpeg_color_space == JCS_CMYK) {
         // libjpeg cannot convert from CMYK to RGB - here we set up
         // so libjpeg will give us CMYK samples back and we will
         // later manually convert them to RGB
         cinfo.out_color_space = JCS_CMYK;
+    } else if (cinfo.jpeg_color_space == JCS_GRAYSCALE) {
+        cinfo.out_color_space = JCS_GRAYSCALE;
+        srcDepth = k8BitGray_SrcDepth;
     } else {
         cinfo.out_color_space = JCS_RGB;
     }
 
-    SkBitmap::Config config = this->getPrefConfig(k32Bit_SrcDepth, false);
+    SkBitmap::Config config = this->getPrefConfig(srcDepth, false);
     // only these make sense for jpegs
-    if (config != SkBitmap::kARGB_8888_Config &&
-        config != SkBitmap::kARGB_4444_Config &&
-        config != SkBitmap::kRGB_565_Config) {
+    if (SkBitmap::kA8_Config == config) {
+        if (cinfo.jpeg_color_space != JCS_GRAYSCALE) {
+            // Converting from a non grayscale image to A8 is
+            // not currently supported.
+            config = SkBitmap::kARGB_8888_Config;
+            // Change the output from jpeg back to RGB.
+            cinfo.out_color_space = JCS_RGB;
+        }
+    } else if (config != SkBitmap::kARGB_8888_Config &&
+               config != SkBitmap::kARGB_4444_Config &&
+               config != SkBitmap::kRGB_565_Config) {
         config = SkBitmap::kARGB_8888_Config;
     }