Revert of Remove unused (by clients) SkUnitMapper (https://codereview.chromium.org/283273002/)

include/core/SkReadBuffer.h

Index: include/core/SkReadBuffer.h
diff --git a/include/core/SkReadBuffer.h b/include/core/SkReadBuffer.h
index e962234ddb6bccf06f2b55f19551cffce2df6115..4da27d4fe0c6902de0a908a3637ebcfe120d2d48 100644
--- a/include/core/SkReadBuffer.h
+++ b/include/core/SkReadBuffer.h
@@ -23,6 +23,7 @@
 #include "SkReader32.h"
 #include "SkRefCnt.h"
 #include "SkShader.h"
+#include "SkUnitMapper.h"
 #include "SkWriteBuffer.h"
 #include "SkXfermode.h"
 
@@ -44,7 +45,6 @@
         kGradientFlippedFlag_Version       = 24,
         kDashWritesPhaseIntervals_Version  = 25,
         kColorShaderNoBool_Version         = 26,
-        kNoUnitMappers_Version             = 27,
     };
 
     /**
@@ -121,13 +121,9 @@
     SkPixelRef*    readPixelRef()    { return this->readFlattenable<SkPixelRef>(); }
     SkRasterizer*  readRasterizer()  { return this->readFlattenable<SkRasterizer>(); }
     SkShader*      readShader()      { return this->readFlattenable<SkShader>(); }
+    SkUnitMapper*  readUnitMapper()  { return this->readFlattenable<SkUnitMapper>(); }
     SkXfermode*    readXfermode()    { return this->readFlattenable<SkXfermode>(); }
 
-    /**
-     *  Like readFlattenable() but explicitly just skips the data that was written for the
-     *  flattenable (or the sentinel that there wasn't one).
-     */
-    virtual void skipFlattenable();
 
     // binary data and arrays
     virtual bool readByteArray(void* value, size_t size);