Harden degenerate gradient context handling

src/effects/gradients/SkLinearGradient.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Sk4fLinearGradient.h"
 #include "SkLinearGradient.h"
 #include "SkRefCnt.h"
@@ skipping 64 matching lines @@
 }
 
 size_t SkLinearGradient::onContextSize(const ContextRec& rec) const {
     return use_4f_context(rec, fGradFlags)
         ? sizeof(LinearGradient4fContext)
         : sizeof(LinearGradientContext);
 }
 
 SkShader::Context* SkLinearGradient::onCreateContext(const ContextRec& rec, void* storage) const {
     return use_4f_context(rec, fGradFlags)
-        ? static_cast<SkShader::Context*>(new (storage) LinearGradient4fContext(*this, rec))
-        : static_cast<SkShader::Context*>(new (storage) LinearGradientContext(*this, rec));
+        ? CheckedCreateContext<LinearGradient4fContext>(storage, *this, rec)
+        : CheckedCreateContext<  LinearGradientContext>(storage, *this, rec);
 }
 
 // This swizzles SkColor into the same component order as SkPMColor, but does not actually
 // "pre" multiply the color components.
 //
 // This allows us to map directly to Sk4f, and eventually scale down to bytes to output a
 // SkPMColor from the floats, without having to swizzle each time.
 //
 static uint32_t SkSwizzle_Color_to_PMColor(SkColor c) {
     return SkPackARGB32NoCheck(SkColorGetA(c), SkColorGetR(c), SkColorGetG(c), SkColorGetB(c));
@@ skipping 663 matching lines @@
             this->shade4_dx_clamp<false, true>(dstC, count, fx, dx, invDx, dither);
         }
     } else {
         if (fApplyAlphaAfterInterp) {
             this->shade4_dx_clamp<true, false>(dstC, count, fx, dx, invDx, dither);
         } else {
             this->shade4_dx_clamp<false, false>(dstC, count, fx, dx, invDx, dither);
         }
     }
 }