Enable subpixel positioning for internal display with dsf larger than 1.0

ui/gfx/font_render_params_linux.cc

Index: ui/gfx/font_render_params_linux.cc
diff --git a/ui/gfx/font_render_params_linux.cc b/ui/gfx/font_render_params_linux.cc
index f02636e8050c2da9466648995aada7952e1f09f6..a198358ecff6e279277157ba31cfa3d3a1ed7304 100644
--- a/ui/gfx/font_render_params_linux.cc
+++ b/ui/gfx/font_render_params_linux.cc
@@ -23,6 +23,12 @@ namespace gfx {
 
 namespace {
 
+#if defined(OS_CHROMEOS)
+// A device scale factor for an internal display (if any)
+// that is used to determine if subpixel positioning should be used.
+float device_scale_factor_for_internal_display = 1.0f;
+#endif
+
 // Keyed by hashes of FontRenderParamQuery structs from
 // HashFontRenderParamsQuery().
 typedef base::MRUCache<uint32, FontRenderParams> Cache;
@@ -43,6 +49,14 @@ struct SynchronizedCache {
 base::LazyInstance<SynchronizedCache>::Leaky g_synchronized_cache =
     LAZY_INSTANCE_INITIALIZER;
 
+bool IsBrowserTextSubpixelPositioningEnabled() {
+#if defined(OS_CHROMEOS)
+  return device_scale_factor_for_internal_display > 1.0f;
+#else
+  return false;
+#endif
+}
+
 // Converts Fontconfig FC_HINT_STYLE to FontRenderParams::Hinting.
 FontRenderParams::Hinting ConvertFontconfigHintStyle(int hint_style) {
   switch (hint_style) {
@@ -176,7 +190,6 @@ FontRenderParams GetFontRenderParams(const FontRenderParamsQuery& query,
   if (delegate)
     params = delegate->GetDefaultFontRenderParams();
   QueryFontconfig(query, &params, family_out);
-
   if (!params.antialiasing) {
     // Cairo forces full hinting when antialiasing is disabled, since anything
     // less than that looks awful; do the same here. Requesting subpixel
@@ -187,10 +200,11 @@ FontRenderParams GetFontRenderParams(const FontRenderParamsQuery& query,
   } else {
     // Fontconfig doesn't support configuring subpixel positioning; check a
     // flag.
-    params.subpixel_positioning = CommandLine::ForCurrentProcess()->HasSwitch(
+    params.subpixel_positioning =
         query.for_web_contents ?
-        switches::kEnableWebkitTextSubpixelPositioning :
-        switches::kEnableBrowserTextSubpixelPositioning);
+        CommandLine::ForCurrentProcess()->HasSwitch(
+            switches::kEnableWebkitTextSubpixelPositioning) :
+        IsBrowserTextSubpixelPositioningEnabled();
 
     // To enable subpixel positioning, we need to disable hinting.
     if (params.subpixel_positioning)
@@ -217,4 +231,10 @@ void ClearFontRenderParamsCacheForTest() {
   synchronized_cache->cache.Clear();
 }
 
+#if defined(OS_CHROMEOS)
+void SetFontRenderParamsDeviceScaleFactor(float device_scale_factor) {
+  device_scale_factor_for_internal_display = device_scale_factor;
+}
+#endif
+
 }  // namespace gfx