Bug 1698336 - Fix high contrast rendering of <meter>. r=mstange

Using the same color for the track and the meter chunk is not going to
fly of course...

In high contrast, make the colors consistent with <progress>, which
seems like a reasonable thing to do.

Differential Revision: https://phabricator.services.mozilla.com/D108347

widget/nsNativeBasicTheme.cpp

@@ -459,8 +459,7 @@ std::pair<sRGBColor, sRGBColor> nsNativeBasicTheme::ComputeProgressTrackColors(
 std::pair<sRGBColor, sRGBColor> nsNativeBasicTheme::ComputeMeterchunkColors(
     const EventStates& aMeterState, UseSystemColors aUseSystemColors) {
   if (bool(aUseSystemColors)) {
-    return SystemColorPair(StyleSystemColor::TextBackground,
-                           StyleSystemColor::TextForeground);
+    return ComputeProgressColors(aUseSystemColors);
   }
   sRGBColor borderColor = sColorMeterGreen20;
   sRGBColor chunkColor = sColorMeterGreen10;
@@ -476,15 +475,6 @@ std::pair<sRGBColor, sRGBColor> nsNativeBasicTheme::ComputeMeterchunkColors(
   return std::make_pair(chunkColor, borderColor);
 }
 
-std::pair<sRGBColor, sRGBColor> nsNativeBasicTheme::ComputeMeterTrackColors(
-    UseSystemColors aUseSystemColors) {
-  if (bool(aUseSystemColors)) {
-    return SystemColorPair(StyleSystemColor::TextBackground,
-                           StyleSystemColor::TextForeground);
-  }
-  return std::make_pair(sColorGrey10, sColorGrey40);
-}
-
 sRGBColor nsNativeBasicTheme::ComputeMenulistArrowButtonColor(
     const EventStates& aState, UseSystemColors aUseSystemColors) {
   bool isDisabled = aState.HasState(NS_EVENT_STATE_DISABLED);
@@ -1322,8 +1312,7 @@ void nsNativeBasicTheme::PaintProgress(nsIFrame* aFrame,
   {
     // Paint the track, unclipped.
     auto [backgroundColor, borderColor] =
-        aIsMeter ? ComputeMeterTrackColors(aUseSystemColors)
-                 : ComputeProgressTrackColors(aUseSystemColors);
+        ComputeProgressTrackColors(aUseSystemColors);
     PaintRoundedRectWithRadius(aPaintData, rect, rect, backgroundColor,
                                borderColor, borderWidth, radius, aDpiRatio);
   }

widget/nsNativeBasicTheme.h

@@ -207,7 +207,6 @@ class nsNativeBasicTheme : protected nsNativeTheme, public nsITheme {
   std::pair<sRGBColor, sRGBColor> ComputeProgressTrackColors(UseSystemColors);
   std::pair<sRGBColor, sRGBColor> ComputeMeterchunkColors(
       const EventStates& aMeterState, UseSystemColors);
-  std::pair<sRGBColor, sRGBColor> ComputeMeterTrackColors(UseSystemColors);
   sRGBColor ComputeMenulistArrowButtonColor(const EventStates&,
                                             UseSystemColors);
   std::array<sRGBColor, 3> ComputeFocusRectColors(UseSystemColors);