Add ability to output ImageBaseGSUrl to render_picture and use in rebaseline server

tools/image_expectations.h

Index: tools/image_expectations.h
diff --git a/tools/image_expectations.h b/tools/image_expectations.h
index ae1df193548f90fec65f73af9e12b722539b6b64..370198ff8f6519244db5061b7f45d48679296d27 100644
--- a/tools/image_expectations.h
+++ b/tools/image_expectations.h
@@ -119,6 +119,13 @@ namespace sk_tools {
         void addDescription(const char *key, const char *value);
 
         /**
+         * Adds the image base Google Storage URL to the summary of results.
+         *
+         * @param imageBaseGSUrl the image base Google Storage URL
+         */
+        void setImageBaseGSUrl(const char *imageBaseGSUrl);
+
+        /**
          * Returns true if this test result matches its expectations.
          * If there are no expectations for this test result, this will return false.
          *
@@ -151,6 +158,7 @@ namespace sk_tools {
         Json::Value fDescriptions;
         Json::Value fExpectedJsonRoot;
         Json::Value fExpectedResults;
+        Json::Value fImageBaseGSUrl;
     };
 
 } // namespace sk_tools