Use removeFontFace to avoid resetting fontSelector.

Source/web/WebSettingsImpl.cpp

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 49 matching lines @@
     , m_clobberUserAgentInitialScaleQuirk(false)
     , m_pinchOverlayScrollbarThickness(0)
     , m_mainFrameResizesAreOrientationChanges(false)
 {
     ASSERT(settings);
 }
 
 void WebSettingsImpl::setStandardFontFamily(const WebString& font, UScriptCode script)
 {
     m_settings->genericFontFamilySettings().setStandard(font, script);
+    m_settings->notifyGenericFontFamilyChange();

[dglazkov, 2014/01/29 05:11:50]

These WebSettingImpl functions are never called separately. Look at the
callsites. They are only called when updating web_preferences wholesale. Why do
we need to traverse the frames tree after each call?

[tasak, 2014/01/29 10:13:43]

I would like to confirm what you mean. As far as I investigated,

(1) Each frame has its own document.
(2) Each document has its own StyleEngine and its own CSSFontSelector.
(3) CSSFontSelector has its own GenericFontFamilySettings (different instance
from WebSettingsImpl).

Each page can have multiple frame -- i.e. iframes.

Looking at caller side, chrome just invokes setSansSerifFontFamilyWrapper and
seems not to recreate renderer or reload page?

So ... how can we update all GenericFontFamilySettings without traversing
document?

I think, you are very familiar with GenericFontFamilySettings things. I need
your help.

 }
 
 void WebSettingsImpl::setFixedFontFamily(const WebString& font, UScriptCode script)
 {
     m_settings->genericFontFamilySettings().setFixed(font, script);
+    m_settings->notifyGenericFontFamilyChange();
 }
 
 void WebSettingsImpl::setSerifFontFamily(const WebString& font, UScriptCode script)
 {
     m_settings->genericFontFamilySettings().setSerif(font, script);
+    m_settings->notifyGenericFontFamilyChange();
 }
 
 void WebSettingsImpl::setSansSerifFontFamily(const WebString& font, UScriptCode script)
 {
     m_settings->genericFontFamilySettings().setSansSerif(font, script);
+    m_settings->notifyGenericFontFamilyChange();
 }
 
 void WebSettingsImpl::setCursiveFontFamily(const WebString& font, UScriptCode script)
 {
     m_settings->genericFontFamilySettings().setCursive(font, script);
+    m_settings->notifyGenericFontFamilyChange();
 }
 
 void WebSettingsImpl::setFantasyFontFamily(const WebString& font, UScriptCode script)
 {
     m_settings->genericFontFamilySettings().setFantasy(font, script);
+    m_settings->notifyGenericFontFamilyChange();
 }
 
 void WebSettingsImpl::setPictographFontFamily(const WebString& font, UScriptCode script)
 {
     m_settings->genericFontFamilySettings().setPictograph(font, script);
+    m_settings->notifyGenericFontFamilyChange();
 }
 
 void WebSettingsImpl::setDefaultFontSize(int size)
 {
     m_settings->setDefaultFontSize(size);
 #if OS(WIN)
     // RenderTheme is a singleton that needs to know the default font size to
     // draw some form controls. We let it know each time the size changes.
     WebCore::RenderThemeChromiumWin::setDefaultFontSize(size);
 #endif
@@ skipping 643 matching lines @@
 {
     m_settings->setUseSolidColorScrollbars(enabled);
 }
 
 void WebSettingsImpl::setMainFrameResizesAreOrientationChanges(bool enabled)
 {
     m_mainFrameResizesAreOrientationChanges = enabled;
 }
 
 } // namespace blink