Add GM that tests GrTextureDomain and fix bug where kDecal_Mode gets incorrectly ignored.

src/gpu/effects/GrTextureDomain.cpp

Index: src/gpu/effects/GrTextureDomain.cpp
diff --git a/src/gpu/effects/GrTextureDomain.cpp b/src/gpu/effects/GrTextureDomain.cpp
index 70d61592245b66d4802f209479923d4ae33c6baf..656000b0595828c4d1c398cfbd658c2c3f4a25ad 100644
--- a/src/gpu/effects/GrTextureDomain.cpp
+++ b/src/gpu/effects/GrTextureDomain.cpp
@@ -16,7 +16,7 @@ GrTextureDomain::GrTextureDomain(const SkRect& domain, Mode mode, int index)
     : fIndex(index) {
 
     static const SkRect kFullRect = {0, 0, SK_Scalar1, SK_Scalar1};
-    if (domain.contains(kFullRect)) {
+    if (domain.contains(kFullRect) && kClamp_Mode == mode) {
         fMode = kIgnore_Mode;
     } else {
         fMode = mode;