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

gm/rebaseline_server/imagepair.py

Index: gm/rebaseline_server/imagepair.py
diff --git a/gm/rebaseline_server/imagepair.py b/gm/rebaseline_server/imagepair.py
index 0ac0c4213883568a01fbbea8cbdae69fd1416f09..e85c21948bfdc6ed683e4cd0977cc8f380d2f7ec 100644
--- a/gm/rebaseline_server/imagepair.py
+++ b/gm/rebaseline_server/imagepair.py
@@ -32,17 +32,19 @@ class ImagePair(object):
   """
 
   def __init__(self, image_diff_db,
-               base_url, imageA_relative_url, imageB_relative_url,
+               imageA_base_url, imageB_base_url,
+               imageA_relative_url, imageB_relative_url,
                expectations=None, extra_columns=None, source_json_file=None,
                download_all_images=False):
     """
     Args:
       image_diff_db: ImageDiffDB instance we use to generate/store image diffs
-      base_url: base of all image URLs
+      imageA_base_url: string; base URL for image A
+      imageB_base_url: string; base URL for image B
       imageA_relative_url: string; URL pointing at an image, relative to
-          base_url; or None, if this image is missing
+          imageA_base_url; or None, if this image is missing
       imageB_relative_url: string; URL pointing at an image, relative to
-          base_url; or None, if this image is missing
+          imageB_base_url; or None, if this image is missing
       expectations: optional dictionary containing expectations-specific
           metadata (ignore-failure, bug numbers, etc.)
       extra_columns: optional dictionary containing more metadata (test name,
@@ -55,7 +57,8 @@ class ImagePair(object):
           (imageA == imageB, or one of them is missing)
     """
     self._image_diff_db = image_diff_db
-    self.base_url = base_url
+    self.imageA_base_url = imageA_base_url
+    self.imageB_base_url = imageB_base_url
     self.imageA_relative_url = imageA_relative_url
     self.imageB_relative_url = imageB_relative_url
     self.expectations_dict = expectations
@@ -76,9 +79,11 @@ class ImagePair(object):
     if self._diff_record != None or download_all_images:
       image_diff_db.add_image_pair(
           expected_image_locator=imageA_relative_url,
-          expected_image_url=self.posixpath_join(base_url, imageA_relative_url),
+          expected_image_url=self.posixpath_join(imageA_base_url,
+                                                 imageA_relative_url),
           actual_image_locator=imageB_relative_url,
-          actual_image_url=self.posixpath_join(base_url, imageB_relative_url))
+          actual_image_url=self.posixpath_join(imageB_base_url,
+                                               imageB_relative_url))
 
   def as_dict(self):
     """Returns a dictionary describing this ImagePair.