Add subsetting to SkScanlineDecoder

include/codec/SkCodec.h

Index: include/codec/SkCodec.h
diff --git a/include/codec/SkCodec.h b/include/codec/SkCodec.h
index 1b9cb0f5d7e3afb73b0fda2dde8a593e55058ed4..89b7b4344591f69fc8340dd876dd6ce23c6cc746 100644
--- a/include/codec/SkCodec.h
+++ b/include/codec/SkCodec.h
@@ -55,20 +55,7 @@ public:
      *  The returned value is the codec's suggestion for the closest valid
      *  scale that it can natively support
      */
-    SkISize getScaledDimensions(float desiredScale) const {
-        // Negative and zero scales are errors.
-        SkASSERT(desiredScale > 0.0f);
-        if (desiredScale <= 0.0f) {
-            return SkISize::Make(0, 0);
-        }
-
-        // Upscaling is not supported. Return the original size if the client
-        // requests an upscale.
-        if (desiredScale >= 1.0f) {
-            return this->getInfo().dimensions();
-        }
-        return this->onGetScaledDimensions(desiredScale);
-    }
+    SkISize getScaledDimensions(float desiredScale) const;
 
     /**
      *  Return (via desiredSubset) a subset which can decoded from this codec,
@@ -85,9 +72,7 @@ public:
      *  @return true if this codec supports decoding desiredSubset (as
      *      returned, potentially modified)
      */
-    bool getValidSubset(SkIRect* desiredSubset) const {
-        return this->onGetValidSubset(desiredSubset);
-    }
+    bool getValidSubset(SkIRect* desiredSubset) const;
 
     /**
      *  Format of the encoded data.
@@ -259,11 +244,11 @@ public:
      *  @return Enum representing success or reason for failure.
      */
     Result startScanlineDecode(const SkImageInfo& dstInfo, const SkCodec::Options* options,
-                 SkPMColor ctable[], int* ctableCount);
+            SkPMColor ctable[], int* ctableCount);
 
     /**
      *  Simplified version of startScanlineDecode() that asserts that info is NOT
-     *  kIndex8_SkColorType and uses the default Options.
+     *  kIndex8_SkColorType and uses the default options.
      */
     Result startScanlineDecode(const SkImageInfo& dstInfo);
 
@@ -398,6 +383,11 @@ protected:
         return this->getInfo().dimensions();
     }
 
+    virtual bool onGetValidSubset(SkIRect* /* desiredSubset */) const {
+        // By default, subsets are not supported.
+        return false;
+    }
+
     // FIXME: What to do about subsets??
     /**
      *  Subclasses should override if they support dimensions other than the
@@ -420,11 +410,6 @@ protected:
                                SkPMColor ctable[], int* ctableCount,
                                int* rowsDecoded) = 0;
 
-    virtual bool onGetValidSubset(SkIRect* /* desiredSubset */) const {
-        // By default, subsets are not supported.
-        return false;
-    }
-
     virtual bool onReallyHasAlpha() const { return false; }
 
     /**