[Themes Service] Implement better default value for which Google logo to use.

chrome/browser/themes/theme_service.cc

Index: chrome/browser/themes/theme_service.cc
diff --git a/chrome/browser/themes/theme_service.cc b/chrome/browser/themes/theme_service.cc
index 1dba96f3942c8ba2eb9da04364133930dcdf980c..b07a456f00d792269ebc7a89639b3c6d99c8fa17 100644
--- a/chrome/browser/themes/theme_service.cc
+++ b/chrome/browser/themes/theme_service.cc
@@ -78,6 +78,19 @@ void WritePackToDiskCallback(BrowserThemePack* pack,
     NOTREACHED() << "Could not write theme pack to disk";
 }
 
+// Heuristic to determine if color is grayscale. This is used to decide whether
+// to use the colorful or white logo, if a theme fails to specify which.
+bool IsColorGrayscale(SkColor color) {
+  const int kChannelTolerance = 9;
+  int r = SkColorGetR(color);
+  int g = SkColorGetG(color);
+  int b = SkColorGetB(color);
+  // range = max(r, g, b) - min(r, g, b).

[pkotwicz, 2014/09/16 03:57:18]

Nit: Use std::max() and std::min(). It makes the code more readable

[huangs, 2014/09/16 15:38:54]

Done.

+  int range = (r > g) ? (r > b ? r : b) - (g < b ? g : b) :
+      (g > b ? g : b) - (r < b ? r : b);
+  return range < kChannelTolerance;
+}
+
 }  // namespace
 
 ThemeService::ThemeService()
@@ -193,12 +206,17 @@ int ThemeService::GetDisplayProperty(int id) const {
     return result;
   }
 
-  if (id == Properties::NTP_LOGO_ALTERNATE &&
-      !UsingDefaultTheme() &&
-      !UsingSystemTheme()) {
-    // Use the alternate logo for themes from the web store except for
-    // |kDefaultThemeGalleryID|.
-    return 1;
+  if (id == Properties::NTP_LOGO_ALTERNATE) {
+    // Use colorful logo for |kDefaultThemeGalleryID| themes.

[pkotwicz, 2014/09/16 03:57:18]

Remove the comment. It no longer makes sense.

[huangs, 2014/09/16 15:38:54]

Done; made the comments more succinct.

+    if (UsingDefaultTheme() || UsingSystemTheme())
+      return 0;
+
+    // Use white logo if background image is used.
+    if (HasCustomImage(IDR_THEME_NTP_BACKGROUND))
+      return 1;
+
+    SkColor background_color = GetColor(Properties::COLOR_NTP_BACKGROUND);
+    return IsColorGrayscale(background_color) ? 0 : 1;
   }
 
   return Properties::GetDefaultDisplayProperty(id);