Remove the majority of uses of GetLuma().

Typically this is to determine a contrasting color or to distinguish light/dark.
There are better fucntions for these purposes.

Bug: 659451
Change-Id: Iad770610ef6b93c75c880badcc2ac9784c74ac12
Reviewed-on: https://chromium-review.googlesource.com/c/1401428
Reviewed-by: Ben Wells <benwells@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621161}

apps/ui/views/app_window_frame_view.cc

@@ -372,13 +372,10 @@ SkColor AppWindowFrameView::CurrentFrameColor() {
 void AppWindowFrameView::SetButtonImagesForFrame() {
   DCHECK(draw_frame_);
 
-  // If the frame is dark, we should use the light images so they have
-  // some contrast.
-  const uint8_t kLumaThreshold = 100;
-  bool use_light = color_utils::GetLuma(CurrentFrameColor()) < kLumaThreshold;
-
+  // If the frame is dark, we should use the light images so they have some
+  // contrast.
   ui::ResourceBundle& rb = ui::ResourceBundle::GetSharedInstance();
-  if (use_light) {
+  if (color_utils::IsDark(CurrentFrameColor())) {
     maximize_button_->SetImage(
         views::Button::STATE_NORMAL,
         rb.GetNativeImageNamed(IDR_APP_WINDOW_MAXIMIZE_L).ToImageSkia());

chrome/browser/web_applications/components/web_app_icon_generator.cc

@@ -41,7 +41,6 @@ class GeneratedIconImageSource : public gfx::CanvasImageSource {
  private:
   // gfx::CanvasImageSource overrides:
   void Draw(gfx::Canvas* canvas) override {
-    const uint8_t kLumaThreshold = 190;
     const int icon_size = output_size_ * 3 / 4;
     const int icon_inset = output_size_ / 8;
     const size_t border_radius = output_size_ / 16;
@@ -64,13 +63,10 @@ class GeneratedIconImageSource : public gfx::CanvasImageSource {
 
     // The text rect's size needs to be odd to center the text correctly.
     gfx::Rect text_rect(icon_inset, icon_inset, icon_size + 1, icon_size + 1);
-    // Draw the letter onto the rounded rect. The letter's color depends on the
-    // luma of |color|.
-    const uint8_t luma = color_utils::GetLuma(color_);
     canvas->DrawStringRectWithFlags(
         base::string16(1, std::toupper(letter_)),
         gfx::FontList(gfx::Font(font_name, font_size)),
-        (luma > kLumaThreshold) ? SK_ColorBLACK : SK_ColorWHITE, text_rect,
+        color_utils::GetColorWithMaxContrast(color_), text_rect,
         gfx::Canvas::TEXT_ALIGN_CENTER);
   }
 

ui/gfx/sys_color_change_listener.cc

@@ -21,16 +21,16 @@ bool g_is_inverted_color_scheme = false;
 bool g_is_inverted_color_scheme_initialized = false;
 
 void UpdateInvertedColorScheme() {
-  const uint8_t foreground_luma =
-      color_utils::GetLuma(color_utils::GetSysSkColor(COLOR_WINDOWTEXT));
-  const uint8_t background_luma =
-      color_utils::GetLuma(color_utils::GetSysSkColor(COLOR_WINDOW));
   HIGHCONTRAST high_contrast = {0};
   high_contrast.cbSize = sizeof(HIGHCONTRAST);
-  g_is_inverted_color_scheme =
+  const bool is_high_contrast =
       SystemParametersInfo(SPI_GETHIGHCONTRAST, 0, &high_contrast, 0) &&
-      ((high_contrast.dwFlags & HCF_HIGHCONTRASTON) != 0) &&
-      foreground_luma > background_luma;
+      ((high_contrast.dwFlags & HCF_HIGHCONTRASTON) != 0);
+  g_is_inverted_color_scheme =
+      is_high_contrast && (color_utils::GetRelativeLuminance(
+                               color_utils::GetSysSkColor(COLOR_WINDOWTEXT)) >
+                           color_utils::GetRelativeLuminance(
+                               color_utils::GetSysSkColor(COLOR_WINDOW)));
   g_is_inverted_color_scheme_initialized = true;
 }