Track when fallback icon color is the default.

components/favicon_base/fallback_icon_url_parser.cc

Index: components/favicon_base/fallback_icon_url_parser.cc
diff --git a/components/favicon_base/fallback_icon_url_parser.cc b/components/favicon_base/fallback_icon_url_parser.cc
index 8855695bfdfb88dd3211a847c6b3fbc1859c1f58..214c88ff9df24caf2f9022fc64da95f593f7456f 100644
--- a/components/favicon_base/fallback_icon_url_parser.cc
+++ b/components/favicon_base/fallback_icon_url_parser.cc
@@ -85,8 +85,13 @@ bool ParsedFallbackIconPath::ParseSpecs(
   if (*size <= 0)
     return false;
 
-  if (!tokens[1].empty() && !ParseColor(tokens[1], &style->background_color))
-    return false;
+  *style = favicon_base::FallbackIconStyle();
+
+  if (!tokens[1].empty()) {
+    style->is_default_background_color = false;
+    if (!ParseColor(tokens[1], &style->background_color))
+      return false;
+  }
 
   if (tokens[2].empty())
     favicon_base::MatchFallbackIconTextColorAgainstBackgroundColor(style);