Use Identity matrix for SkTransparentShader.

src/core/SkBlitter.cpp

Index: src/core/SkBlitter.cpp
diff --git a/src/core/SkBlitter.cpp b/src/core/SkBlitter.cpp
index a86881ad3784c9857c7005a3f66fb53ddcaac4ee..cb84ec7d9db0aaa75f8539f7789fba8a5090bc70 100644
--- a/src/core/SkBlitter.cpp
+++ b/src/core/SkBlitter.cpp
@@ -996,7 +996,8 @@ SkBlitter* SkBlitter::Choose(const SkBitmap& device,
 class SkTransparentShaderContext : public SkShader::Context {
 public:
     SkTransparentShaderContext(const SkShader& shader, const SkShader::ContextRec& rec)
-        : INHERITED(shader, rec) {}
+        // Override rec with the identity matrix, so it is guaranteed to be invertible.
+        : INHERITED(shader, SkShader::ContextRec(*rec.fDevice, *rec.fPaint, SkMatrix::I())) {}
 
     virtual void shadeSpan(int x, int y, SkPMColor colors[], int count) SK_OVERRIDE {
         sk_bzero(colors, count * sizeof(SkPMColor));