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

tools/image_expectations.cpp

Index: tools/image_expectations.cpp
diff --git a/tools/image_expectations.cpp b/tools/image_expectations.cpp
index dfc2638a9e28406c70994111c8a09b7a17f95c14..7eba70f8d5ac5ff5782cc2ee61a601c6c1fa01da 100644
--- a/tools/image_expectations.cpp
+++ b/tools/image_expectations.cpp
@@ -30,6 +30,7 @@
 const static char kJsonKey_ActualResults[] = "actual-results";
 const static char kJsonKey_Descriptions[] = "descriptions";
 const static char kJsonKey_ExpectedResults[] = "expected-results";
+const static char kJsonKey_ImageBaseGSUrl[] = "image-base-gs-url";
 const static char kJsonKey_Header[] = "header";
 const static char kJsonKey_Header_Type[] = "type";
 const static char kJsonKey_Header_Revision[] = "revision";
@@ -182,6 +183,10 @@ namespace sk_tools {
         fDescriptions[key] = value;
     }
 
+    void ImageResultsAndExpectations::setImageBaseGSUrl(const char *imageBaseGSUrl) {
+        fImageBaseGSUrl = imageBaseGSUrl;
+    }
+
     bool ImageResultsAndExpectations::matchesExpectation(const char *sourceName,
                                                          const ImageDigest &digest,
                                                          const int *tileNumber) {
@@ -213,6 +218,7 @@ namespace sk_tools {
         root[kJsonKey_ActualResults] = fActualResults;
         root[kJsonKey_Descriptions] = fDescriptions;
         root[kJsonKey_Header] = header;
+        root[kJsonKey_ImageBaseGSUrl] = fImageBaseGSUrl;
         std::string jsonStdString = root.toStyledString();
         SkFILEWStream stream(filename);
         stream.write(jsonStdString.c_str(), jsonStdString.length());