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

src/effects/gradients/SkLinearGradient.cpp

Index: src/effects/gradients/SkLinearGradient.cpp
diff --git a/src/effects/gradients/SkLinearGradient.cpp b/src/effects/gradients/SkLinearGradient.cpp
index b24a6349c73cc4f94910159cb8f3a06f67aec79a..e660d7cd2d6ae936795805085eb89a89601f6113 100644
--- a/src/effects/gradients/SkLinearGradient.cpp
+++ b/src/effects/gradients/SkLinearGradient.cpp
@@ -71,12 +71,24 @@
     buffer.writePoint(fEnd);
 }
 
-bool SkLinearGradient::setContext(const SkBitmap& device, const SkPaint& paint,
-                                 const SkMatrix& matrix) {
-    if (!this->INHERITED::setContext(device, paint, matrix)) {
-        return false;
-    }
-
+size_t SkLinearGradient::contextSize() const {
+    return sizeof(LinearGradientContext);
+}
+
+SkShader::Context* SkLinearGradient::createContext(const SkBitmap& device, const SkPaint& paint,
+                                                   const SkMatrix& matrix, void* storage) const {
+    if (!this->validContext(device, paint, matrix)) {
+        return NULL;
+    }
+
+    return SkNEW_PLACEMENT_ARGS(storage, LinearGradientContext, (*this, device, paint, matrix));
+}
+
+SkLinearGradient::LinearGradientContext::LinearGradientContext(
+        const SkLinearGradient& shader, const SkBitmap& device,
+        const SkPaint& paint, const SkMatrix& matrix)
+    : INHERITED(shader, device, paint, matrix)
+{
     unsigned mask = SkMatrix::kTranslate_Mask | SkMatrix::kScale_Mask;
     if ((fDstToIndex.getType() & ~mask) == 0) {
         // when we dither, we are (usually) not const-in-Y
@@ -87,7 +99,6 @@
             fFlags |= SkShader::kConstInY16_Flag;
         }
     }
-    return true;
 }
 
 #define NO_CHECK_ITER               \
@@ -196,14 +207,16 @@
 
 }
 
-void SkLinearGradient::shadeSpan(int x, int y, SkPMColor* SK_RESTRICT dstC,
-                                int count) {
+void SkLinearGradient::LinearGradientContext::shadeSpan(int x, int y, SkPMColor* SK_RESTRICT dstC,
+                                                        int count) {
     SkASSERT(count > 0);
+
+    const SkLinearGradient& linearGradient = static_cast<const SkLinearGradient&>(fShader);
 
     SkPoint             srcPt;
     SkMatrix::MapXYProc dstProc = fDstToIndexProc;
-    TileProc            proc = fTileProc;
-    const SkPMColor* SK_RESTRICT cache = this->getCache32();
+    TileProc            proc = linearGradient.fTileProc;
+    const SkPMColor* SK_RESTRICT cache = fCache->getCache32();
     int                 toggle = init_dither_toggle(x, y);
 
     if (fDstToIndexClass != kPerspective_MatrixClass) {
@@ -223,12 +236,12 @@
         LinearShadeProc shadeProc = shadeSpan_linear_repeat;
         if (0 == dx) {
             shadeProc = shadeSpan_linear_vertical_lerp;
-        } else if (SkShader::kClamp_TileMode == fTileMode) {
+        } else if (SkShader::kClamp_TileMode == linearGradient.fTileMode) {
             shadeProc = shadeSpan_linear_clamp;
-        } else if (SkShader::kMirror_TileMode == fTileMode) {
+        } else if (SkShader::kMirror_TileMode == linearGradient.fTileMode) {
             shadeProc = shadeSpan_linear_mirror;
         } else {
-            SkASSERT(SkShader::kRepeat_TileMode == fTileMode);
+            SkASSERT(SkShader::kRepeat_TileMode == linearGradient.fTileMode);
         }
         (*shadeProc)(proc, dx, fx, dstC, cache, toggle, count);
     } else {
@@ -381,14 +394,16 @@
     return SkAbs32(x) < (SK_Fixed1 >> 12);
 }
 
-void SkLinearGradient::shadeSpan16(int x, int y,
-                                  uint16_t* SK_RESTRICT dstC, int count) {
+void SkLinearGradient::LinearGradientContext::shadeSpan16(int x, int y,
+                                                          uint16_t* SK_RESTRICT dstC, int count) {
     SkASSERT(count > 0);
+
+    const SkLinearGradient& linearGradient = static_cast<const SkLinearGradient&>(fShader);
 
     SkPoint             srcPt;
     SkMatrix::MapXYProc dstProc = fDstToIndexProc;
-    TileProc            proc = fTileProc;
-    const uint16_t* SK_RESTRICT cache = this->getCache16();
+    TileProc            proc = linearGradient.fTileProc;
+    const uint16_t* SK_RESTRICT cache = fCache->getCache16();
     int                 toggle = init_dither_toggle16(x, y);
 
     if (fDstToIndexClass != kPerspective_MatrixClass) {
@@ -408,12 +423,12 @@
         LinearShade16Proc shadeProc = shadeSpan16_linear_repeat;
         if (fixed_nearly_zero(dx)) {
             shadeProc = shadeSpan16_linear_vertical;
-        } else if (SkShader::kClamp_TileMode == fTileMode) {
+        } else if (SkShader::kClamp_TileMode == linearGradient.fTileMode) {
             shadeProc = shadeSpan16_linear_clamp;
-        } else if (SkShader::kMirror_TileMode == fTileMode) {
+        } else if (SkShader::kMirror_TileMode == linearGradient.fTileMode) {
             shadeProc = shadeSpan16_linear_mirror;
         } else {
-            SkASSERT(SkShader::kRepeat_TileMode == fTileMode);
+            SkASSERT(SkShader::kRepeat_TileMode == linearGradient.fTileMode);
         }
         (*shadeProc)(proc, dx, fx, dstC, cache, toggle, count);
     } else {