Qualify the return value of SkImageDecoder::decode

Add a new enum to differentiate between a complete decode and a
partial decode (with the third value being failure). Return this
value from SkImageDecoder::onDecode (in all subclasses, plus
SkImageDecoder_empty) and ::decode.

For convenience, if the enum is treated as a boolean, success and
partial success are both considered true.

Note that the static helper functions (DecodeFile etc) still return
true and false (for one thing, this allows us to continue to use
SkImageDecoder::DecodeMemory as an SkPicture::InstallPixelRefProc in
SkPicture::CreateFromStream).

Also correctly report failure in SkASTCImageDecoder::onDecode when
SkTextureCompressor::DecompressBufferFromFormat fails.

BUG=skia:3037
BUG:b/17419670

Review URL: https://codereview.chromium.org/647023006

1 files changed, 1 insertions, 1 deletions

diff --git a/samplecode/SampleUnpremul.cpp b/samplecode/SampleUnpremul.cpp
index 992444d05d..ffe4428b48 100644
--- a/samplecode/SampleUnpremul.cpp
+++ b/samplecode/SampleUnpremul.cpp
@@ -182,7 +182,7 @@ private:
             decoder->setRequireUnpremultipliedColors(true);
         }
         fDecodeSucceeded = decoder->decode(&stream, &fBitmap, kN32_SkColorType,
-                                           SkImageDecoder::kDecodePixels_Mode);
+                SkImageDecoder::kDecodePixels_Mode) != SkImageDecoder::kFailure;
         this->inval(NULL);
     }