Gradient shaders: make fPtsToUnit const, pre-cache getType().

src/effects/gradients/SkGradientShaderPriv.h

Index: src/effects/gradients/SkGradientShaderPriv.h
diff --git a/src/effects/gradients/SkGradientShaderPriv.h b/src/effects/gradients/SkGradientShaderPriv.h
index 72014d330e5e5503035f95fb2d2f95bbf5bf17dd..125c7b056d681a8782b1029037dc5ea4504abaf6 100644
--- a/src/effects/gradients/SkGradientShaderPriv.h
+++ b/src/effects/gradients/SkGradientShaderPriv.h
@@ -121,7 +121,7 @@ public:
     };
 
 public:
-    SkGradientShaderBase(const Descriptor& desc);
+    SkGradientShaderBase(const Descriptor& desc, const SkMatrix& ptsToUnit);
     virtual ~SkGradientShaderBase();
 
     // The cache is initialized on-demand when getCache16/32 is called.
@@ -223,7 +223,7 @@ protected:
     virtual void flatten(SkWriteBuffer&) const SK_OVERRIDE;
     SK_TO_STRING_OVERRIDE()
 
-    SkMatrix    fPtsToUnit;     // set by subclass
+    const SkMatrix fPtsToUnit;
     TileMode    fTileMode;
     TileProc    fTileProc;
     int         fColorCount;