Make SkPngCodec decode progressively.

src/codec/SkIcoCodec.cpp

Index: src/codec/SkIcoCodec.cpp
diff --git a/src/codec/SkIcoCodec.cpp b/src/codec/SkIcoCodec.cpp
index 0e81b72407218778b9d469e72b95941149b83309..9d622c202b2ff862b23b113b249d1d95c3bf4153 100644
--- a/src/codec/SkIcoCodec.cpp
+++ b/src/codec/SkIcoCodec.cpp
@@ -186,6 +186,7 @@ SkIcoCodec::SkIcoCodec(int width, int height, const SkEncodedInfo& info,
     : INHERITED(width, height, info, nullptr)
     , fEmbeddedCodecs(codecs)
     , fCurrScanlineCodec(nullptr)
+    , fCurrIncrementalCodec(nullptr)
 {}
 
 /*
@@ -289,6 +290,7 @@ SkCodec::Result SkIcoCodec::onStartScanlineDecode(const SkImageInfo& dstInfo,
         result = embeddedCodec->startScanlineDecode(dstInfo, &options, colorTable, colorCount);
         if (kSuccess == result) {
             fCurrScanlineCodec = embeddedCodec;
+            fCurrIncrementalCodec = nullptr;
             return result;
         }
 
@@ -309,13 +311,64 @@ bool SkIcoCodec::onSkipScanlines(int count) {
     return fCurrScanlineCodec->skipScanlines(count);
 }
 
+SkCodec::Result SkIcoCodec::onStartIncrementalDecode(const SkImageInfo& dstInfo,
+        const SkCodec::Options& options, SkPMColor* colorTable, int* colorCount) {
+    int index = 0;
+    while (true) {
+        index = this->chooseCodec(dstInfo.dimensions(), index);
+        if (index < 0) {
+            break;
+        }
+
+        SkCodec* embeddedCodec = fEmbeddedCodecs->operator[](index);
+        if (SkCodec::kSuccess == embeddedCodec->startIncrementalDecode(dstInfo,
+                &options, colorTable, colorCount)) {
+            fCurrIncrementalCodec = embeddedCodec;
+            fCurrScanlineCodec = nullptr;
+            return SkCodec::kSuccess;
+        }
+
+        index++;
+    }
+
+    // FIXME: As long as PNG only supports incremental decode and BMP only
+    // supports scanline decoding, which image the client gets depends on
+    // which entry point they use, meaning getScaledDimensions could return
+    // a set of dimensions that is only supported by one or the other.
+    SkCodecPrintf("Error: No matching candidate image in ico.\n");
+    return kInvalidScale;
+}
+
+SkCodec::Result SkIcoCodec::onIncrementalDecode(std::function<void*(int)> callback,
+                                                int* rowsDecoded) {
+    SkASSERT(fCurrIncrementalCodec);
+    return fCurrIncrementalCodec->incrementalDecode(callback, rowsDecoded);
+}
+
 SkCodec::SkScanlineOrder SkIcoCodec::onGetScanlineOrder() const {
     // FIXME: This function will possibly return the wrong value if it is called
-    //        before startScanlineDecode().
-    return fCurrScanlineCodec ? fCurrScanlineCodec->getScanlineOrder() :
-            INHERITED::onGetScanlineOrder();
+    //        before startScanlineDecode()/startIncrementalDecode().
+    if (fCurrScanlineCodec) {
+        SkASSERT(!fCurrIncrementalCodec);
+        return fCurrScanlineCodec->getScanlineOrder();
+    }
+
+    if (fCurrIncrementalCodec) {
+        return fCurrIncrementalCodec->getScanlineOrder();
+    }
+
+    return INHERITED::onGetScanlineOrder();
 }
 
 SkSampler* SkIcoCodec::getSampler(bool createIfNecessary) {
-    return fCurrScanlineCodec ? fCurrScanlineCodec->getSampler(createIfNecessary) : nullptr;
+    if (fCurrScanlineCodec) {
+        SkASSERT(!fCurrIncrementalCodec);
+        return fCurrScanlineCodec->getSampler(createIfNecessary);
+    }
+
+    if (fCurrIncrementalCodec) {
+        return fCurrIncrementalCodec->getSampler(createIfNecessary);
+    }
+
+    return nullptr;
 }