allow createScalerContext to return null, and then have the GDI backend trigger that if we fail to …

src/core/SkScalerContext.cpp

Index: src/core/SkScalerContext.cpp
diff --git a/src/core/SkScalerContext.cpp b/src/core/SkScalerContext.cpp
index 521cb9b6b1ae28e70c6bcf9d97186650b5692c25..65873c683f7cd771854e25a5bc895d11d6df772c 100644
--- a/src/core/SkScalerContext.cpp
+++ b/src/core/SkScalerContext.cpp
@@ -852,14 +852,14 @@ protected:
 
 extern SkScalerContext* SkCreateColorScalerContext(const SkDescriptor* desc);
 
-SkScalerContext* SkTypeface::createScalerContext(const SkDescriptor* desc) const {
-    SkScalerContext* c = NULL;  //SkCreateColorScalerContext(desc);
-    if (NULL == c) {
-        c = this->onCreateScalerContext(desc);
-    }
-    if (NULL == c) {
+SkScalerContext* SkTypeface::createScalerContext(const SkDescriptor* desc,
+                                                 bool allowFailure) const {
+    SkScalerContext* c = this->onCreateScalerContext(desc);
+
+    if (!c && !allowFailure) {
         c = SkNEW_ARGS(SkScalerContext_Empty,
                        (const_cast<SkTypeface*>(this), desc));
     }
     return c;
 }
+