return null if subshader fails

src/core/SkFilterShader.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkFilterShader.h"
 
 #include "SkColorFilter.h"
@@ skipping 40 matching lines @@
     // if the filter might change alpha, clear the opaque flag in the shader
     if (!(filterF & SkColorFilter::kAlphaUnchanged_Flag)) {
         shaderF &= ~(SkShader::kOpaqueAlpha_Flag | SkShader::kHasSpan16_Flag);
     }
     return shaderF;
 }
 
 SkShader::Context* SkFilterShader::onCreateContext(const ContextRec& rec, void* storage) const {
     char* shaderContextStorage = (char*)storage + sizeof(FilterShaderContext);
     SkShader::Context* shaderContext = fShader->createContext(rec, shaderContextStorage);
-    SkASSERT(shaderContext);
-
+    if (NULL == shaderContext) {
+        return NULL;
+    }
     return SkNEW_PLACEMENT_ARGS(storage, FilterShaderContext, (*this, shaderContext, rec));
 }
 
 size_t SkFilterShader::contextSize() const {
     return sizeof(FilterShaderContext) + fShader->contextSize();
 }
 
 SkFilterShader::FilterShaderContext::FilterShaderContext(const SkFilterShader& filterShader,
                                                          SkShader::Context* shaderContext,
                                                          const ContextRec& rec)
@@ skipping 28 matching lines @@
     str->append("Shader: ");
     fShader->toString(str);
     str->append(" Filter: ");
     // TODO: add "fFilter->toString(str);" once SkColorFilter::toString is added
 
     this->INHERITED::toString(str);
 
     str->append(")");
 }
 #endif