Initialize SkColor variables in ThemeBackgroundInfo.

Bug: 977430, 991220
Change-Id: Ic29ba69d4f896b99afd9ad174ea5187cb56cf892
TBR: sky@chromium.org
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1739489Reviewed-by: Balazs Engedy <engedy@chromium.org>
Commit-Queue: Balazs Engedy <engedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684373}

chrome/common/search/instant_types.h

@@ -74,13 +74,13 @@ struct ThemeBackgroundInfo {
   std::string collection_id;
 
   // The theme background color. Always valid.
-  SkColor background_color;
+  SkColor background_color = gfx::kPlaceholderColor;
 
   // The theme text color.
-  SkColor text_color;
+  SkColor text_color = gfx::kPlaceholderColor;
 
   // The theme text color light.
-  SkColor text_color_light;
+  SkColor text_color_light = gfx::kPlaceholderColor;
 
   // The theme id for the theme background image.
   // Value is only valid if there's a custom theme background image.