Remove dependency on SkJsonCanvas.h

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1748183007
NOTRY=True

Review URL: https://codereview.chromium.org/1748183007
diff --git a/tools/debugger/SkDrawCommand.h b/tools/debugger/SkDrawCommand.h
index 74c2b2c..a2835dc 100644
--- a/tools/debugger/SkDrawCommand.h
+++ b/tools/debugger/SkDrawCommand.h
@@ -113,6 +113,10 @@
 
     static const char* GetCommandString(OpType type);
 
+    // Helper methods for converting things to JSON
+    static Json::Value MakeJsonIRect(const SkIRect&);
+    static Json::Value MakeJsonMatrix(const SkMatrix&);
+
 protected:
     SkTDArray<SkString*> fInfo;