cast -1 to Mode to avoid warning (enum compared to signed int)

git-svn-id: http://skia.googlecode.com/svn/trunk/src@12580 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gpu/effects/GrTextureDomain.cpp b/gpu/effects/GrTextureDomain.cpp
index 517eb6d..70d6159 100644
--- a/gpu/effects/GrTextureDomain.cpp
+++ b/gpu/effects/GrTextureDomain.cpp
@@ -45,7 +45,7 @@
                                               const SkString& inCoords,
                                               const GrGLEffect::TextureSampler sampler,
                                               const char* inModulateColor) {
-    SkASSERT(-1 == fMode || textureDomain.mode() == fMode);
+    SkASSERT((Mode)-1 == fMode || textureDomain.mode() == fMode);
     SkDEBUGCODE(fMode = textureDomain.mode();)
 
     if (kIgnore_Mode == textureDomain.mode()) {