Fill incomplete images in SkCodec parent class

Rather than implementing some sort of "fill" in every
SkCodec subclass for incomplete images, let's make the
parent class handle this situation.

This includes an API change to SkCodec.h

SkCodec::getScanlines() now returns the number of lines it
read successfully, rather than an SkCodec::Result enum.
getScanlines() most often fails on an incomplete input, in
which case it is useful to know how many lines were
successfully decoded - this provides more information than
kIncomplete vs kSuccess.  We do lose information when the
API is used improperly, as we are no longer able to return
kInvalidParameter or kScanlineNotStarted.

Known Issues:
Does not work for incomplete fFrameIsSubset gifs.
Does not work for incomplete icos.

BUG=skia:

Review URL: https://codereview.chromium.org/1332053002

1 files changed, 6 insertions, 2 deletions

diff --git a/src/codec/SkCodec_libpng.h b/src/codec/SkCodec_libpng.h
index 3a16cc6813..6bdf58065b 100644
--- a/src/codec/SkCodec_libpng.h
+++ b/src/codec/SkCodec_libpng.h
@@ -32,16 +32,20 @@ public:
     virtual ~SkPngCodec();
 
 protected:
-    Result onGetPixels(const SkImageInfo&, void*, size_t, const Options&, SkPMColor*, int*)
+    Result onGetPixels(const SkImageInfo&, void*, size_t, const Options&, SkPMColor*, int*, int*)
             override;
     SkEncodedFormat onGetEncodedFormat() const override { return kPNG_SkEncodedFormat; }
     bool onRewind() override;
+    uint32_t onGetFillValue(SkColorType colorType, SkAlphaType alphaType) const override;
     bool onReallyHasAlpha() const final;
 
     // Helper to set up swizzler and color table. Also calls png_read_update_info.
     Result initializeSwizzler(const SkImageInfo& requestedInfo, const Options&,
                               SkPMColor*, int* ctableCount);
-    SkSampler* getSampler() override { return fSwizzler; }
+    SkSampler* getSampler(bool createIfNecessary) override {
+        SkASSERT(fSwizzler);
+        return fSwizzler;
+    }
 
     SkPngCodec(const SkImageInfo&, SkStream*, png_structp, png_infop, int, int);