[QT] Ensure background tab text color has sufficient contrast

Since the frame color depends on `use_custom_frame`, the background tab
text color needs to be computed based on the frame color.  For this,
BlendForMinContrast with default settings (formerly GetReadableColor)
is used.

R=thestig

Change-Id: I5178ffb44f4c3de9015b7cb973fddfb9a430411e
Bug: 1317782
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4113991
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1084746}

ui/qt/qt_ui.cc

@@ -24,6 +24,7 @@
 #include "ui/color/color_mixer.h"
 #include "ui/color/color_provider.h"
 #include "ui/color/color_recipe.h"
+#include "ui/color/color_transform.h"
 #include "ui/gfx/color_palette.h"
 #include "ui/gfx/color_utils.h"
 #include "ui/gfx/font.h"
@@ -438,9 +439,6 @@ void QtUi::AddNativeColorMixer(ui::ColorProvider* provider,
       {ui::kColorNativeHeaderSeparatorBorderInactive, ColorType::kMidground,
        ColorState::kInactive},
       {ui::kColorNativeLabelForeground, ColorType::kWindowFg},
-      {ui::kColorNativeTabForegroundInactiveFrameActive, ColorType::kButtonFg},
-      {ui::kColorNativeTabForegroundInactiveFrameInactive, ColorType::kButtonFg,
-       ColorState::kInactive},
       {ui::kColorNativeTextfieldBorderUnfocused, ColorType::kMidground,
        ColorState::kInactive},
       {ui::kColorNativeToolbarBackground, ColorType::kButtonBg},
@@ -454,6 +452,13 @@ void QtUi::AddNativeColorMixer(ui::ColorProvider* provider,
       shim_->GetFrameColor(ColorState::kNormal, use_custom_frame)};
   mixer[ui::kColorFrameInactive] = {
       shim_->GetFrameColor(ColorState::kInactive, use_custom_frame)};
+
+  const SkColor button_fg =
+      shim_->GetColor(ColorType::kButtonFg, ColorState::kNormal);
+  mixer[ui::kColorNativeTabForegroundInactiveFrameActive] =
+      ui::BlendForMinContrast({button_fg}, {ui::kColorFrameActive});
+  mixer[ui::kColorNativeTabForegroundInactiveFrameInactive] =
+      ui::BlendForMinContrast({button_fg}, {ui::kColorFrameInactive});
 }
 
 DISABLE_CFI_VCALL