Updates subpixel positioning and hinting when DSF is changed

ash/display/display_manager.cc

Index: ash/display/display_manager.cc
diff --git a/ash/display/display_manager.cc b/ash/display/display_manager.cc
index b83a34528613589ea935b03ef8f0d75b205c5afc..194c1cb4e99c0005b2f395d081ab568ef26bec1a 100644
--- a/ash/display/display_manager.cc
+++ b/ash/display/display_manager.cc
@@ -111,6 +111,40 @@ void MaybeInitInternalDisplay(int64 id) {
     gfx::Display::SetInternalDisplayId(id);
 }
 
+class FontRenderParamsRewriterAsh : public gfx::FontRenderParamsRewriter {
+ public:
+  FontRenderParamsRewriterAsh() {}
+  ~FontRenderParamsRewriterAsh() override {}
+
+ private:
+  bool IsBrowserTextSubpixelPositioningEnabled() {
+    DisplayManager* display_manager = Shell::GetInstance()->display_manager();
+    if (!display_manager->HasInternalDisplay())
+      return false;
+    int64 internal_id = gfx::Display::InternalDisplayId();
+    const gfx::Display& internal_display =
+        display_manager->GetDisplayForId(internal_id);
+    // The internal display ID exists but the display object does not exist in
+    // case of the docked mode.
+    if (!internal_display.is_valid())
+      return false;
+    const DisplayInfo& display_info =
+        display_manager->GetDisplayInfo(internal_id);
+    return display_info.GetEffectiveDeviceScaleFactor() > 1.0f;
+  }
+
+  // gfx::FontRenderParamsRewriter:
+  void RewriteParams(gfx::FontRenderParams* params) override {
+#if defined(OS_CHROMEOS)
+    if (params->antialiasing) {
+      params->subpixel_positioning = IsBrowserTextSubpixelPositioningEnabled();
+      if (params->subpixel_positioning)
+        params->hinting = gfx::FontRenderParams::HINTING_NONE;
+    }
+#endif
+  }
+};
+
 }  // namespace
 
 using std::string;
@@ -152,10 +186,7 @@ DisplayManager::DisplayManager()
 }
 
 DisplayManager::~DisplayManager() {
-#if defined(OS_CHROMEOS)
-  // Reset the font params.
-  gfx::SetFontRenderParamsDeviceScaleFactor(1.0f);
-#endif
+  gfx::FontRenderParamsRewriter::Shutdown();
 }
 
 // static
@@ -238,14 +269,7 @@ void DisplayManager::InitDefaultDisplay() {
 }
 
 void DisplayManager::InitFontParams() {
-#if defined(OS_CHROMEOS)
-  if (!HasInternalDisplay())
-    return;
-  const DisplayInfo& display_info =
-      GetDisplayInfo(gfx::Display::InternalDisplayId());
-  gfx::SetFontRenderParamsDeviceScaleFactor(
-      display_info.GetEffectiveDeviceScaleFactor());
-#endif  // OS_CHROMEOS
+  gfx::FontRenderParamsRewriter::SetInstance(new FontRenderParamsRewriterAsh());
 }
 
 // static