Skip per-script font preferences registration and filling on Android.

chrome/browser/chrome_content_browser_client.cc

Index: chrome/browser/chrome_content_browser_client.cc
diff --git a/chrome/browser/chrome_content_browser_client.cc b/chrome/browser/chrome_content_browser_client.cc
index 49fe6b1d5b98ce3b0175ac24ff087f3c7d82b582..271e03a7024cceff40edba4aee42ae4c790a2cee 100644
--- a/chrome/browser/chrome_content_browser_client.cc
+++ b/chrome/browser/chrome_content_browser_client.cc
@@ -479,6 +479,8 @@ bool CertMatchesFilter(const net::X509Certificate& cert,
 void FillFontFamilyMap(const PrefService* prefs,
                        const char* map_name,
                        webkit_glue::ScriptFontFamilyMap* map) {
+  // TODO: Get rid of the brute-force scan over possible (font family / script)
+  // combinations - see http://crbug.com/308095.
   for (size_t i = 0; i < prefs::kWebKitScriptsForFontFamilyMapsLength; ++i) {
     const char* script = prefs::kWebKitScriptsForFontFamilyMaps[i];
     std::string pref_name = base::StringPrintf("%s.%s", map_name, script);
@@ -2090,6 +2092,10 @@ void ChromeContentBrowserClient::OverrideWebkitPrefs(
       rvh->GetProcess()->GetBrowserContext());
   PrefService* prefs = profile->GetPrefs();
 
+  // Fill per-script font preferences. These are not available on Android and
+  // filling the maps is CPU intensive (http://crbug.com/308033). The ifdef can
+  // be removed after http://crbug.com/308095 is solved.
+#if !defined(OS_ANDROID)

[Yaron, 2013/10/16 16:24:13]

Theres' some related code in chrome/browser/ui/prefs/prefs_tab_helper.cc to
actually register all of these prefs. Happens once on startup but takes over
10ms last I recall. If we're removing the read of these prefs, can we also
remove the registration?

[ppi, 2013/10/16 18:02:36]

Thanks for the pointer! Actually, it looks like the registration of observers
for these preferences was already disabled for Android by Marcus:
https://chromiumcodereview.appspot.com/12529014 .

[Yaron, 2013/10/16 18:08:53]

Ya, I measured after the observers were removed. We still register >1k prefs

   FillFontFamilyMap(prefs, prefs::kWebKitStandardFontFamilyMap,
                     &web_prefs->standard_font_family_map);
   FillFontFamilyMap(prefs, prefs::kWebKitFixedFontFamilyMap,
@@ -2104,6 +2110,7 @@ void ChromeContentBrowserClient::OverrideWebkitPrefs(
                     &web_prefs->fantasy_font_family_map);
   FillFontFamilyMap(prefs, prefs::kWebKitPictographFontFamilyMap,
                     &web_prefs->pictograph_font_family_map);
+#endif
 
   web_prefs->default_font_size =
       prefs->GetInteger(prefs::kWebKitDefaultFontSize);