libgtk2ui: cast gdk_color components to fix compilation under gcc 4.7.2

I was getting this error before this patch:

    error: narrowing conversion of ‘(((color >> 16) & 255u) * 257u)’ from ‘SkColor {aka unsigned int}’ to ‘guint16 {aka short unsigned int}’ inside { } is ill-formed in C++11 [-Werror=narrowing]

BUG=130810

Review URL: https://chromiumcodereview.appspot.com/12684005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@188351 0039d316-1c4b-4281-b951-d872f2087c98

AUTHORS

@@ -231,3 +231,4 @@ Johannes Rudolph <johannes.rudolph@googlemail.com>
 Aaron Jacobs <samusaaron3@gmail.com>
 Sam Larison <qufighter@gmail.com>
 Jun Jiang <jun.a.jiang@intel.com>
+Bobby Powers <bobbypowers@gmail.com>

chrome/browser/ui/libgtk2ui/skia_utils_gtk2.cc

@@ -22,9 +22,9 @@ SkColor GdkColorToSkColor(GdkColor color) {
 GdkColor SkColorToGdkColor(SkColor color) {
   GdkColor gdk_color = {
       0,
-      SkColorGetR(color) * kSkiaToGDKMultiplier,
-      SkColorGetG(color) * kSkiaToGDKMultiplier,
-      SkColorGetB(color) * kSkiaToGDKMultiplier
+      static_cast<guint16>(SkColorGetR(color) * kSkiaToGDKMultiplier),
+      static_cast<guint16>(SkColorGetG(color) * kSkiaToGDKMultiplier),
+      static_cast<guint16>(SkColorGetB(color) * kSkiaToGDKMultiplier)
   };
   return gdk_color;
 }