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, 7 insertions, 4 deletions

diff --git a/src/codec/SkBmpMaskCodec.h b/src/codec/SkBmpMaskCodec.h
index 1c44c7fb40..1c1d1d8c11 100644
--- a/src/codec/SkBmpMaskCodec.h
+++ b/src/codec/SkBmpMaskCodec.h
@@ -36,7 +36,7 @@ protected:
 
     Result onGetPixels(const SkImageInfo& dstInfo, void* dst,
                        size_t dstRowBytes, const Options&, SkPMColor*,
-                       int*) override;
+                       int*, int*) override;
 
     SkCodec::Result prepareToDecode(const SkImageInfo& dstInfo,
             const SkCodec::Options& options, SkPMColor inputColorPtr[],
@@ -45,10 +45,13 @@ protected:
 private:
 
     bool initializeSwizzler(const SkImageInfo& dstInfo);
-    SkSampler* getSampler() override { return fMaskSwizzler; }
+    SkSampler* getSampler(bool createIfNecessary) override {
+        SkASSERT(fMaskSwizzler);
+        return fMaskSwizzler;
+    }
 
-    Result decodeRows(const SkImageInfo& dstInfo, void* dst, size_t dstRowBytes,
-                      const Options& opts) override;
+    int decodeRows(const SkImageInfo& dstInfo, void* dst, size_t dstRowBytes,
+            const Options& opts) override;
 
     SkAutoTDelete<SkMasks>              fMasks;        // owned
     SkAutoTDelete<SkMaskSwizzler>       fMaskSwizzler;