Introduce text blob processing but don't wire it up

Have all the old code paths start using lists in preparation
for introducing text blobs.

Change-Id: I65cc02ee3da63bc3c9492db78a08b0eee3b1f931
Reviewed-on: https://skia-review.googlesource.com/141081
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Herb Derby <herb@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
diff --git a/include/core/SkTextBlob.h b/include/core/SkTextBlob.h
index 672cc20..c68ad41 100644
--- a/include/core/SkTextBlob.h
+++ b/include/core/SkTextBlob.h
@@ -14,6 +14,7 @@
 #include "SkString.h"
 #include "SkRefCnt.h"
 
+class SkGlyphRunList;
 class SkReadBuffer;
 class SkWriteBuffer;
 
@@ -107,6 +108,7 @@
         fCacheID.store(cacheID);
     }
 
+    friend class SkGlyphRunList;
     friend class GrTextBlobCache;
     friend class SkTextBlobBuilder;
     friend class SkTextBlobRunIterator;