Fix assertion failure in SkGpuDevice from 8412.



git-svn-id: http://skia.googlecode.com/svn/trunk@8413 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/gpu/SkGpuDevice.cpp b/src/gpu/SkGpuDevice.cpp
index ad65d17..6f6608a 100644
--- a/src/gpu/SkGpuDevice.cpp
+++ b/src/gpu/SkGpuDevice.cpp
@@ -484,7 +484,7 @@
     SkXfermode::Coeff dm = SkXfermode::kISA_Coeff;
 
     SkXfermode* mode = skPaint.getXfermode();
-    GrEffectRef* xferEffect;
+    GrEffectRef* xferEffect = NULL;
     if (SkXfermode::AsNewEffect(mode, dev->context(), &xferEffect, &sm, &dm)) {
         // We're not ready for xfermode effects yet
         GrAssert(NULL == xferEffect);