color_utils cleanup:

* Attempt to define and standardize usage of "luma" vs. "(relative) luminance" vs. "lightness", at least as far as color_utils functions, comments, and direct callers are concerned.  Especially the first two terms are often both called "luminance" (universally, not just in Chrome code), so the distinction is confusing.
* Misc. cleanups to make caller code shorter or clearer.
* Naming consistency: remove "Get" from function names where we're not doing some simple "getter" operation, but rather computing a value.
* Modify some caller behaviors to be hopefully-more-correct
* Note that GetReadableColor() can accept values with alpha, it will just ignore the alpha.
* Add a PickContrastingColor() function, which is basically a subset of GetReadableColor().  This will be useful for an upcoming change where we want to choose between two fixed colors instead of luma-inverting a single input.
* Use more precise multipliers in Luma().

BUG=none
TEST=none

Review URL: https://codereview.chromium.org/1761183002

Cr-Commit-Position: refs/heads/master@{#379643}

1 files changed, 2 insertions, 4 deletions

diff --git a/apps/ui/views/app_window_frame_view.cc b/apps/ui/views/app_window_frame_view.cc
index 4b6246b..728e038 100644
--- a/apps/ui/views/app_window_frame_view.cc
+++ b/apps/ui/views/app_window_frame_view.cc
@@ -374,10 +374,8 @@ void AppWindowFrameView::SetButtonImagesForFrame() {
 
   // If the frame is dark, we should use the light images so they have
   // some contrast.
-  unsigned char frame_luma =
-      color_utils::GetLuminanceForColor(CurrentFrameColor());
-  const unsigned char kLuminanceThreshold = 100;
-  bool use_light = frame_luma < kLuminanceThreshold;
+  const uint8_t kLumaThreshold = 100;
+  bool use_light = color_utils::GetLuma(CurrentFrameColor()) < kLumaThreshold;
 
   ui::ResourceBundle& rb = ui::ResourceBundle::GetSharedInstance();
   if (use_light) {