Use light instead of no-preference for printing.

We use a preferred color-scheme of light for screens. When we decided to
not use dark for printing we chose no-preference, but content depends on
color-scheme to either be light or dark since that is the case for
screen media. This matches what both Firefox and Safari does.

Bug: 1086441
Change-Id: I1b10c76068ca9cfebf0d991c342b15f99185698e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2216770Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#771997}

third_party/blink/renderer/core/css/style_engine.cc

@@ -2118,7 +2118,7 @@ void StyleEngine::UpdateColorScheme() {
     preferred_color_scheme_ = PreferredColorScheme::kNoPreference;
   }
   if (GetDocument().Printing())
-    preferred_color_scheme_ = PreferredColorScheme::kNoPreference;
+    preferred_color_scheme_ = PreferredColorScheme::kLight;
   if (forced_colors_ != old_forced_colors ||
       preferred_color_scheme_ != old_preferred_color_scheme)
     PlatformColorsChanged();

third_party/blink/renderer/core/css/style_engine_test.cc

@@ -2667,7 +2667,12 @@ TEST_F(StyleEngineTest, PrintNoDarkColorScheme) {
   GetDocument().body()->setInnerHTML(R"HTML(
     <style>
       :root { color-scheme: dark }
-      body { color: green; }
+      @media (prefers-color-scheme: light) {
+        body { color: green; }
+      }
+      @media (prefers-color-scheme: no-preference) {
+        body { color: orange; }
+      }
       @media (prefers-color-scheme: dark) {
         body { color: red; }
       }