add support for new bitmapshader context

src/core/SkComposeShader.cpp

Index: src/core/SkComposeShader.cpp
diff --git a/src/core/SkComposeShader.cpp b/src/core/SkComposeShader.cpp
index 46ff4019fc22f323649699146f3ba8695f34c3f6..57f0989e2d65b83c500b9b705e66b9485c6fdabe 100644
--- a/src/core/SkComposeShader.cpp
+++ b/src/core/SkComposeShader.cpp
@@ -31,9 +31,9 @@ SkComposeShader::~SkComposeShader() {
 }
 
 size_t SkComposeShader::contextSize(const ContextRec& rec) const {
-    return sizeof(ComposeShaderContext)
-        + fShaderA->contextSize(rec)
-        + fShaderB->contextSize(rec);
+    return SkAlign16(sizeof(ComposeShaderContext))
+         + SkAlign16(fShaderA->contextSize(rec))
+         + SkAlign16(fShaderB->contextSize(rec));
 }
 
 class SkAutoAlphaRestore {
@@ -76,8 +76,8 @@ template <typename T> void safe_call_destructor(T* obj) {
 }
 
 SkShader::Context* SkComposeShader::onCreateContext(const ContextRec& rec, void* storage) const {
-    char* aStorage = (char*) storage + sizeof(ComposeShaderContext);
-    char* bStorage = aStorage + fShaderA->contextSize(rec);
+    char* aStorage = (char*) storage + SkAlign16(sizeof(ComposeShaderContext));
+    char* bStorage = aStorage + SkAlign16(fShaderA->contextSize(rec));
 
     // we preconcat our localMatrix (if any) with the device matrix
     // before calling our sub-shaders