Implement scaling in SkCodecImageGenerator

Plumb calls down to SkCodec.

Add a gm

Change-Id: I16da24eb739295ab72f487df02f19968151443f3
Reviewed-on: https://skia-review.googlesource.com/6287
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>
diff --git a/src/codec/SkCodecImageGenerator.h b/src/codec/SkCodecImageGenerator.h
index 222923b..e1aa220 100644
--- a/src/codec/SkCodecImageGenerator.h
+++ b/src/codec/SkCodecImageGenerator.h
@@ -6,6 +6,7 @@
  */
 
 #include "SkCodec.h"
+#include "SkColorTable.h"
 #include "SkData.h"
 #include "SkImageGenerator.h"
 
@@ -30,6 +31,10 @@
 
     bool onGetYUV8Planes(const SkYUVSizeInfo&, void* planes[3]) override;
 
+    bool onComputeScaledDimensions(SkScalar, SupportedSizes*) override;
+
+    bool onGenerateScaledPixels(const SkPixmap&) override;
+
 private:
     /*
      * Takes ownership of codec
@@ -38,6 +43,7 @@
 
     std::unique_ptr<SkCodec> fCodec;
     sk_sp<SkData> fData;
+    sk_sp<SkColorTable> fColorTable;
 
     typedef SkImageGenerator INHERITED;
 };