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

src/core/SkFilterShader.cpp

Index: src/core/SkFilterShader.cpp
diff --git a/src/core/SkFilterShader.cpp b/src/core/SkFilterShader.cpp
index 58961913c8e4148396f50c8fd4a682804407164f..5c5e8f317c020997ec4ca8b2ba7524fd275b4239 100644
--- a/src/core/SkFilterShader.cpp
+++ b/src/core/SkFilterShader.cpp
@@ -38,9 +38,11 @@ void SkFilterShader::flatten(SkWriteBuffer& buffer) const {
     buffer.writeFlattenable(fFilter);
 }
 
-uint32_t SkFilterShader::getFlags() {
-    uint32_t shaderF = fShader->getFlags();
-    uint32_t filterF = fFilter->getFlags();
+uint32_t SkFilterShader::FilterShaderContext::getFlags() const {
+    const SkFilterShader& filterShader = static_cast<const SkFilterShader&>(fShader);
+
+    uint32_t shaderF = fShaderContext->getFlags();
+    uint32_t filterF = filterShader.fFilter->getFlags();
 
     // if the filter doesn't support 16bit, clear the matching bit in the shader
     if (!(filterF & SkColorFilter::kHasFilter16_Flag)) {
@@ -53,38 +55,62 @@ uint32_t SkFilterShader::getFlags() {
     return shaderF;
 }
 
-bool SkFilterShader::setContext(const SkBitmap& device,
-                                const SkPaint& paint,
-                                const SkMatrix& matrix) {
-    // we need to keep the setContext/endContext calls balanced. If we return
-    // false, our endContext() will not be called.
-
-    if (!this->INHERITED::setContext(device, paint, matrix)) {
-        return false;
-    }
-    if (!fShader->setContext(device, paint, matrix)) {
-        this->INHERITED::endContext();
-        return false;
+SkShader::Context* SkFilterShader::createContext(const SkBitmap& device,
+                                                 const SkPaint& paint,
+                                                 const SkMatrix& matrix,
+                                                 void* storage) const {
+    if (!this->validContext(device, paint, matrix)) {
+        return NULL;
     }
-    return true;
+
+    char* shaderContextStorage = (char*)storage + sizeof(FilterShaderContext);
+    SkShader::Context* shaderContext = fShader->createContext(device, paint, matrix,
+                                                              shaderContextStorage);
+    SkASSERT(shaderContext);
+
+    return SkNEW_PLACEMENT_ARGS(storage, FilterShaderContext,
+                                (*this, shaderContext, device, paint, matrix));
+}
+
+size_t SkFilterShader::contextSize() const {
+    return sizeof(FilterShaderContext) + fShader->contextSize();
+}
+
+bool SkFilterShader::validContext(const SkBitmap& device,
+                                  const SkPaint& paint,
+                                  const SkMatrix& matrix,
+                                  SkMatrix* totalInverse) const {
+    return this->INHERITED::validContext(device, paint, matrix, totalInverse) &&
+           fShader->validContext(device, paint, matrix);
 }
 
-void SkFilterShader::endContext() {
-    fShader->endContext();
-    this->INHERITED::endContext();
+SkFilterShader::FilterShaderContext::FilterShaderContext(const SkFilterShader& filterShader,
+                                                         SkShader::Context* shaderContext,
+                                                         const SkBitmap& device,
+                                                         const SkPaint& paint,
+                                                         const SkMatrix& matrix)
+    : INHERITED(filterShader, device, paint, matrix)
+    , fShaderContext(shaderContext) {}
+
+SkFilterShader::FilterShaderContext::~FilterShaderContext() {
+    fShaderContext->~Context();
 }
 
-void SkFilterShader::shadeSpan(int x, int y, SkPMColor result[], int count) {
-    fShader->shadeSpan(x, y, result, count);
-    fFilter->filterSpan(result, count, result);
+void SkFilterShader::FilterShaderContext::shadeSpan(int x, int y, SkPMColor result[], int count) {
+    const SkFilterShader& filterShader = static_cast<const SkFilterShader&>(fShader);
+
+    fShaderContext->shadeSpan(x, y, result, count);
+    filterShader.fFilter->filterSpan(result, count, result);
 }
 
-void SkFilterShader::shadeSpan16(int x, int y, uint16_t result[], int count) {
-    SkASSERT(fShader->getFlags() & SkShader::kHasSpan16_Flag);
-    SkASSERT(fFilter->getFlags() & SkColorFilter::kHasFilter16_Flag);
+void SkFilterShader::FilterShaderContext::shadeSpan16(int x, int y, uint16_t result[], int count) {
+    const SkFilterShader& filterShader = static_cast<const SkFilterShader&>(fShader);
+
+    SkASSERT(fShaderContext->getFlags() & SkShader::kHasSpan16_Flag);
+    SkASSERT(filterShader.fFilter->getFlags() & SkColorFilter::kHasFilter16_Flag);
 
-    fShader->shadeSpan16(x, y, result, count);
-    fFilter->filterSpan16(result, count, result);
+    fShaderContext->shadeSpan16(x, y, result, count);
+    filterShader.fFilter->filterSpan16(result, count, result);
 }
 
 #ifndef SK_IGNORE_TO_STRING