Try 2: Completely redo how themes are stored on disk and processed at install time.

chrome/browser/browser_theme_provider_mac.mm

Index: chrome/browser/browser_theme_provider_mac.mm
diff --git a/chrome/browser/browser_theme_provider_mac.mm b/chrome/browser/browser_theme_provider_mac.mm
index 65c2182ee23cc4962204a4c7a5d68182fdff5f14..ec3d4a8bcf83dc4b92c03072006c02046c0dffb5 100644
--- a/chrome/browser/browser_theme_provider_mac.mm
+++ b/chrome/browser/browser_theme_provider_mac.mm
@@ -8,6 +8,7 @@
 
 #include "app/gfx/color_utils.h"
 #include "base/logging.h"
+#include "chrome/browser/browser_theme_pack.h"
 #include "skia/ext/skia_utils_mac.h"
 
 namespace {
@@ -75,9 +76,8 @@ NSColor* BrowserThemeProvider::GetNSColor(int id) const {
   if (nscolor_iter != nscolor_cache_.end())
     return nscolor_iter->second;
 
-  ColorMap::const_iterator color_iter = colors_.find(GetColorKey(id));
-  if (color_iter != colors_.end()) {
-    const SkColor& sk_color = color_iter->second;
+  SkColor sk_color;
+  if (theme_pack_.get() && theme_pack_->GetColor(id, &sk_color)) {
     NSColor* color = [NSColor
         colorWithCalibratedRed:SkColorGetR(sk_color)/255.0
                          green:SkColorGetG(sk_color)/255.0
@@ -102,9 +102,8 @@ NSColor* BrowserThemeProvider::GetNSColorTint(int id) const {
   if (nscolor_iter != nscolor_cache_.end())
     return nscolor_iter->second;
 
-  TintMap::const_iterator tint_iter = tints_.find(GetTintKey(id));
-  if (tint_iter != tints_.end()) {
-    color_utils::HSL tint = tint_iter->second;
+  color_utils::HSL tint;
+  if (theme_pack_.get() && theme_pack_->GetTint(id, &tint)) {
     CGFloat hue, saturation, brightness;
     HSLToHSB(tint, &hue, &saturation, &brightness);