Breakup GetAuraColor() to Make Control Flow Obvious

This change moves long switch statements into separate helper functions
to make it easier to see GetAuraColor's control flow.

BUG=

Change-Id: I203ee8dc54020e4ce60924511363a5cb19269e26
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2108821
Commit-Queue: Robert Liao <robliao@chromium.org>
Auto-Submit: Robert Liao <robliao@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#751721}

ui/native_theme/common_theme.cc

@@ -5,6 +5,7 @@
 #include "ui/native_theme/common_theme.h"
 
 #include "base/logging.h"
+#include "base/optional.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/gfx/canvas.h"
@@ -17,15 +18,11 @@
 
 namespace ui {
 
-SkColor GetAuraColor(NativeTheme::ColorId color_id,
-                     const NativeTheme* base_theme,
-                     NativeTheme::ColorScheme color_scheme) {
-  if (color_scheme == NativeTheme::ColorScheme::kDefault)
-    color_scheme = base_theme->GetDefaultSystemColorScheme();
+namespace {
 
-  // High contrast overrides the normal colors for certain ColorIds to be much
-  // darker or lighter.
-  if (base_theme->UsesHighContrastColors()) {
+base::Optional<SkColor> GetHighContrastColor(
+    NativeTheme::ColorId color_id,
+    NativeTheme::ColorScheme color_scheme) {
   switch (color_id) {
     case NativeTheme::kColorId_ButtonUncheckedColor:
     case NativeTheme::kColorId_MenuBorderColor:
@@ -42,18 +39,17 @@ SkColor GetAuraColor(NativeTheme::ColorId color_id,
                  ? gfx::kGoogleBlue100
                  : gfx::kGoogleBlue900;
     default:
-        break;
-    }
+      return base::nullopt;
   }
+}
 
-  if (color_scheme == NativeTheme::ColorScheme::kDark) {
+base::Optional<SkColor> GetDarkSchemeColor(NativeTheme::ColorId color_id) {
   switch (color_id) {
     // Dialogs
     case NativeTheme::kColorId_WindowBackground:
     case NativeTheme::kColorId_DialogBackground:
     case NativeTheme::kColorId_BubbleBackground:
-        return color_utils::AlphaBlend(SK_ColorWHITE, gfx::kGoogleGrey900,
-                                       0.04f);
+      return color_utils::AlphaBlend(SK_ColorWHITE, gfx::kGoogleGrey900, 0.04f);
     case NativeTheme::kColorId_DialogForeground:
       return gfx::kGoogleGrey500;
     case NativeTheme::kColorId_BubbleFooterBackground:
@@ -103,8 +99,7 @@ SkColor GetAuraColor(NativeTheme::ColorId color_id,
 
     // Dropdown
     case NativeTheme::kColorId_DropdownBackgroundColor:
-        return color_utils::AlphaBlend(SK_ColorWHITE, gfx::kGoogleGrey900,
-                                       0.04f);
+      return color_utils::AlphaBlend(SK_ColorWHITE, gfx::kGoogleGrey900, 0.04f);
     case NativeTheme::kColorId_DropdownForegroundColor:
       return gfx::kGoogleGrey200;
     case NativeTheme::kColorId_DropdownSelectedForegroundColor:
@@ -143,8 +138,7 @@ SkColor GetAuraColor(NativeTheme::ColorId color_id,
     // Table
     case NativeTheme::kColorId_TableBackground:
     case NativeTheme::kColorId_TableBackgroundAlternate:
-        return color_utils::AlphaBlend(SK_ColorWHITE, gfx::kGoogleGrey900,
-                                       0.04f);
+      return color_utils::AlphaBlend(SK_ColorWHITE, gfx::kGoogleGrey900, 0.04f);
     case NativeTheme::kColorId_TableText:
     case NativeTheme::kColorId_TableSelectedText:
     case NativeTheme::kColorId_TableSelectedTextUnfocused:
@@ -155,8 +149,7 @@ SkColor GetAuraColor(NativeTheme::ColorId color_id,
     case NativeTheme::kColorId_TextfieldSelectionColor:
       return gfx::kGoogleGrey200;
     case NativeTheme::kColorId_TextfieldReadOnlyBackground: {
-        return color_utils::AlphaBlend(SK_ColorWHITE, gfx::kGoogleGrey900,
-                                       0.04f);
+      return color_utils::AlphaBlend(SK_ColorWHITE, gfx::kGoogleGrey900, 0.04f);
     }
     case NativeTheme::kColorId_TextfieldSelectionBackgroundFocused:
       return gfx::kGoogleBlue800;
@@ -167,8 +160,7 @@ SkColor GetAuraColor(NativeTheme::ColorId color_id,
 
     // Tree
     case NativeTheme::kColorId_TreeBackground:
-        return color_utils::AlphaBlend(SK_ColorWHITE, gfx::kGoogleGrey900,
-                                       0.04f);
+      return color_utils::AlphaBlend(SK_ColorWHITE, gfx::kGoogleGrey900, 0.04f);
     case NativeTheme::kColorId_TreeText:
     case NativeTheme::kColorId_TreeSelectedText:
     case NativeTheme::kColorId_TreeSelectedTextUnfocused:
@@ -189,10 +181,13 @@ SkColor GetAuraColor(NativeTheme::ColorId color_id,
     case NativeTheme::kColorId_DefaultIconColor:
       return gfx::kGoogleGrey500;
     default:
-        break;
-    }
+      return base::nullopt;
   }
+}
 
+SkColor GetDefaultColor(NativeTheme::ColorId color_id,
+                        const NativeTheme* base_theme,
+                        NativeTheme::ColorScheme color_scheme) {
   constexpr SkColor kPrimaryTextColor = gfx::kGoogleGrey900;
 
 
@@ -495,11 +490,38 @@ SkColor GetAuraColor(NativeTheme::ColorId color_id,
           NativeTheme::kColorId_BubbleFooterBackground);
 
     case NativeTheme::kColorId_NumColors:
-      break;
-  }
-
+      // Keeping the kColorId_NumColors case instead of using the default case
+      // allows ColorId additions to trigger compile error for an incomplete
+      // switch enumeration.
       NOTREACHED();
       return gfx::kPlaceholderColor;
+  }
+}
+
+}  // namespace
+
+SkColor GetAuraColor(NativeTheme::ColorId color_id,
+                     const NativeTheme* base_theme,
+                     NativeTheme::ColorScheme color_scheme) {
+  if (color_scheme == NativeTheme::ColorScheme::kDefault)
+    color_scheme = base_theme->GetDefaultSystemColorScheme();
+
+  // High contrast overrides the normal colors for certain ColorIds to be much
+  // darker or lighter.
+  if (base_theme->UsesHighContrastColors()) {
+    base::Optional<SkColor> color =
+        GetHighContrastColor(color_id, color_scheme);
+    if (color.has_value())
+      return color.value();
+  }
+
+  if (color_scheme == NativeTheme::ColorScheme::kDark) {
+    base::Optional<SkColor> color = GetDarkSchemeColor(color_id);
+    if (color.has_value())
+      return color.value();
+  }
+
+  return GetDefaultColor(color_id, base_theme, color_scheme);
 }
 
 void CommonThemePaintMenuItemBackground(