Teach grit that file.svg is an SVG.

grit/format/html_inline.py

Index: grit/format/html_inline.py
diff --git a/grit/format/html_inline.py b/grit/format/html_inline.py
index c2b898e1e0cdbf2d303b3a5bf99a47230f26a80b..66a957aec776199bdd3bc07c94f77b95e070be1b 100755
--- a/grit/format/html_inline.py
+++ b/grit/format/html_inline.py
@@ -22,8 +22,10 @@ from grit import util
 # There is a python bug that makes mimetypes crash if the Windows
 # registry contains non-Latin keys ( http://bugs.python.org/issue9291
 # ). Initing manually and blocking external mime-type databases will
-# prevent that bug and still give us the data we need.
+# prevent that bug and if we add svg manually, it will still give us
+# the data we need.
 mimetypes.init([])
+mimetypes.add_type('image/svg+xml', '.svg')
 
 DIST_DEFAULT = 'chromium'
 DIST_ENV_VAR = 'CHROMIUM_BUILD'
@@ -52,17 +54,6 @@ _ICON_RE = lazy_re.compile(
     re.MULTILINE)
 
 
-
-def FixupMimeType(mime_type):
-  """Helper function that normalizes platform differences in the mime type
-     returned by the Python's mimetypes.guess_type API.
-  """
-  mappings = {
-    'image/x-png': 'image/png'
-  }
-  return mappings[mime_type] if mime_type in mappings else mime_type
-
-
 def GetDistribution():
   """Helper function that gets the distribution we are building.
 
@@ -115,7 +106,10 @@ def SrcInlineAsDataURL(
   if names_only:
     return ""
 
-  mimetype = FixupMimeType(mimetypes.guess_type(filename)[0]) or 'text/plain'
+  mimetype = mimetypes.guess_type(filename)[0]
+  if mimetype is None:
+    raise Exception('%s is of an an unknown type and '
+                    'cannot be stored in a data url.' % filename)
   inline_data = base64.standard_b64encode(util.ReadFile(filepath, util.BINARY))
 
   prefix = src_match.string[src_match.start():src_match.start('filename')]