SkTextBlob plumbing

Add SkTextBlob serialization + drawTextBlob() overrides.

R=mtklein@google.com, reed@google.com, robertphillips@google.com
BUG=269080

Author: fmalita@chromium.org

Review URL: https://codereview.chromium.org/499413002
diff --git a/src/utils/debugger/SkDrawCommand.h b/src/utils/debugger/SkDrawCommand.h
index ce7b1f5..f3c8cca 100644
--- a/src/utils/debugger/SkDrawCommand.h
+++ b/src/utils/debugger/SkDrawCommand.h
@@ -436,6 +436,21 @@
     typedef SkDrawCommand INHERITED;
 };
 
+class SkDrawTextBlobCommand : public SkDrawCommand {
+public:
+    SkDrawTextBlobCommand(const SkTextBlob* blob, SkScalar x, SkScalar y, const SkPaint& paint);
+
+    virtual void execute(SkCanvas* canvas) SK_OVERRIDE;
+
+private:
+    SkAutoTUnref<const SkTextBlob> fBlob;
+    SkScalar                       fXPos;
+    SkScalar                       fYPos;
+    SkPaint                        fPaint;
+
+    typedef SkDrawCommand INHERITED;
+};
+
 class SkDrawRectCommand : public SkDrawCommand {
 public:
     SkDrawRectCommand(const SkRect& rect, const SkPaint& paint);