Add SK_API to SkTextBlob and SkTextBlobBuilder.

include/core/SkTextBlob.h

Index: include/core/SkTextBlob.h
diff --git a/include/core/SkTextBlob.h b/include/core/SkTextBlob.h
index d1b2e0fe1b94f83159869251de19fadc79d5e395..fcf1766c3ee1898a4fffce64121e462f9fc8f8b1 100644
--- a/include/core/SkTextBlob.h
+++ b/include/core/SkTextBlob.h
@@ -17,7 +17,7 @@
 
     SkTextBlob combines multiple text runs into an immutable, ref-counted structure.
 */
-class SkTextBlob : public SkRefCnt {
+class SK_API SkTextBlob : public SkRefCnt {
 public:
     /**
      *  Returns the blob bounding box.
@@ -87,7 +87,7 @@ private:
 
     Helper class for constructing SkTextBlobs.
  */
-class SkTextBlobBuilder {
+class SK_API SkTextBlobBuilder {
 public:
     /**
      *  @param runs The number of runs to be added, if known. This is a storage hint and