Specify Fixed Background Tab Colors in the IncreasedContrastThemeSupplier

The IncreasedContrastThemeSupplier previously had these colors:

                     Frame        Tab Bkgnd   Contrast
                     Color        Text           Ratio
Light Mode Inactive  Gray         Black           5.92
Light Mode Active    Dark Gray    Black           2.15
Dark Mode Inactive   Gray         White           3.54
Dark Mode Active     Dark Gray    White           9.73

This doesn't really make sense as the frame color doesn't change with
light/dark mode. Previously, this worked accidentally as
BlendForMinContrast would save us. After http://crrev.com/687315 , the
IncreasedContrastThemeSupplier was no longer blended, revealing the bug.

Since the frame color is invariant with respect to light/dark mode, the
new colors are as follows:

                     Frame        Tab Bkgnd   Contrast
                     Color        Text           Ratio
Light Mode Inactive  Gray         Black           5.92
Light Mode Active    Dark Gray    White           9.73
Dark Mode Inactive   Gray         Black           5.92
Dark Mode Active     Dark Gray    White           9.73

BUG=1046818

Change-Id: Ic9452154f833f471a51e2ea6eacfb49f10cf1232
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2042144Reviewed-by: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Robert Liao <robliao@chromium.org>
Auto-Submit: Robert Liao <robliao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#739237}

chrome/browser/themes/increased_contrast_theme_supplier.cc

@@ -19,10 +19,12 @@ bool IncreasedContrastThemeSupplier::GetColor(int id, SkColor* color) const {
       *color = foreground;
       return true;
     case ThemeProperties::COLOR_BACKGROUND_TAB_TEXT:
-    case ThemeProperties::COLOR_BACKGROUND_TAB_TEXT_INACTIVE:
     case ThemeProperties::COLOR_BACKGROUND_TAB_TEXT_INCOGNITO:
+      *color = SK_ColorWHITE;
+      return true;
+    case ThemeProperties::COLOR_BACKGROUND_TAB_TEXT_INACTIVE:
     case ThemeProperties::COLOR_BACKGROUND_TAB_TEXT_INCOGNITO_INACTIVE:
-      *color = foreground;
+      *color = SK_ColorBLACK;
       return true;
     case ThemeProperties::COLOR_TOOLBAR:
       *color = background;