Extract most of the mutable state of SkShader into a separate Context object.

SkShader currently stores some state during draw calls via setContext(...).
Move that mutable state into a separate SkShader::Context class that is
constructed on demand for the duration of the draw.

Calls to setContext() are replaced with createContext() which returns a context
corresponding to the shader object or NULL if the parameters to createContext
are invalid.

TEST=out/Debug/dm
BUG=skia:1976
R=scroggo@google.com, skyostil@chromium.org, tomhudson@chromium.org, senorblanco@chromium.org, reed@google.com, bungeman@google.com

Author: dominikg@chromium.org

Review URL: https://codereview.chromium.org/207683004

git-svn-id: http://skia.googlecode.com/svn/trunk@14216 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/effects/gradients/SkSweepGradient.h b/src/effects/gradients/SkSweepGradient.h
index ca19da2..9998ed1 100644
--- a/src/effects/gradients/SkSweepGradient.h
+++ b/src/effects/gradients/SkSweepGradient.h
@@ -14,8 +14,23 @@
 class SkSweepGradient : public SkGradientShaderBase {
 public:
     SkSweepGradient(SkScalar cx, SkScalar cy, const Descriptor&);
-    virtual void shadeSpan(int x, int y, SkPMColor dstC[], int count) SK_OVERRIDE;
-    virtual void shadeSpan16(int x, int y, uint16_t dstC[], int count) SK_OVERRIDE;
+
+    virtual SkShader::Context* createContext(const SkBitmap&, const SkPaint&, const SkMatrix&,
+                                             void* storage) const SK_OVERRIDE;
+    virtual size_t contextSize() const SK_OVERRIDE;
+
+    class SweepGradientContext : public SkGradientShaderBase::GradientShaderBaseContext {
+    public:
+        SweepGradientContext(const SkSweepGradient& shader, const SkBitmap& device,
+                             const SkPaint& paint, const SkMatrix& matrix);
+        ~SweepGradientContext() {}
+
+        virtual void shadeSpan(int x, int y, SkPMColor dstC[], int count) SK_OVERRIDE;
+        virtual void shadeSpan16(int x, int y, uint16_t dstC[], int count) SK_OVERRIDE;
+
+    private:
+        typedef SkGradientShaderBase::GradientShaderBaseContext INHERITED;
+    };
 
     virtual BitmapType asABitmap(SkBitmap* bitmap,
                                  SkMatrix* matrix,
@@ -33,8 +48,9 @@
     virtual void flatten(SkWriteBuffer& buffer) const SK_OVERRIDE;
 
 private:
-    typedef SkGradientShaderBase INHERITED;
     const SkPoint fCenter;
+
+    typedef SkGradientShaderBase INHERITED;
 };
 
 #endif