add support for new bitmapshader context

src/core/SkShader.cpp

Index: src/core/SkShader.cpp
diff --git a/src/core/SkShader.cpp b/src/core/SkShader.cpp
index e36df5b5af057df6fcacdff6277e3e7f8d667c46..5fb441a5c31a6c5dff4ed3248c5c3a535aef5e8a 100644
--- a/src/core/SkShader.cpp
+++ b/src/core/SkShader.cpp
@@ -86,6 +86,9 @@ bool SkShader::asLuminanceColor(SkColor* colorPtr) const {
 }
 
 SkShader::Context* SkShader::createContext(const ContextRec& rec, void* storage) const {
+    // We currently require 16byte alignment for some of our subclasses, so assert that here.
+    SkASSERT(SkIsAlign16((intptr_t)storage));
+
     if (!this->computeTotalInverse(rec, nullptr)) {
         return nullptr;
     }