Add font_scale_factor_quirk pref.

content/renderer/web_preferences.cc

Index: content/renderer/web_preferences.cc
diff --git a/content/renderer/web_preferences.cc b/content/renderer/web_preferences.cc
index 17d4a9c2344df2af9ca9bb35f95c9b2e6687083d..89788276616369c48561d3af0cf9af67e5bf032c 100644
--- a/content/renderer/web_preferences.cc
+++ b/content/renderer/web_preferences.cc
@@ -16,6 +16,10 @@
 #include "third_party/icu/source/common/unicode/uscript.h"
 #include "webkit/common/webpreferences.h"
 
+#if defined(OS_ANDROID)
+#include "ui/gfx/android/device_display_info.h"
+#endif
+
 using WebKit::WebNetworkStateNotifier;
 using WebKit::WebRuntimeFeatures;
 using WebKit::WebSettings;
@@ -109,6 +113,35 @@ void ApplyFontsFromMap(const webkit_glue::ScriptFontFamilyMap& map,
   }
 }
 
+#if defined(OS_ANDROID)
+
+const float kMinFSM = 1.05f;
+const int kWidthForMinFSM = 320;
+const float kMaxFSM = 1.3f;
+const int kWidthForMaxFSM = 800;
+
+float GetFontScaleMultiplier(const WebPreferences& prefs) {
+  if (prefs.font_scale_factor_quirk) {
+    // The value of font_scale_factor passed by Chrome for Android already
+    // includes the multiplier.
+    return 1.0;
+  }
+  gfx::DeviceDisplayInfo info;
+  int minWidth = info.GetSmallestDIPWidth();

[jamesr, 2013/10/21 17:58:33]

we shouldn't be doing logic like this here in the renderer - set up the value in
the browser process

+
+  if (minWidth <= kWidthForMinFSM)
+    return kMinFSM;
+  if (minWidth >= kWidthForMaxFSM)
+    return kMaxFSM;
+
+  // The font scale multiplier varies linearly between kMinFSM and kMaxFSM.
+  float ratio = static_cast<float>(minWidth - kWidthForMinFSM) /
+      (kWidthForMaxFSM - kWidthForMinFSM);
+  return ratio * (kMaxFSM - kMinFSM) + kMinFSM;
+}
+
+#endif  // defined(OS_ANDROID)
+
 }  // namespace
 
 void ApplyWebPreferences(const WebPreferences& prefs, WebView* web_view) {
@@ -324,7 +357,8 @@ void ApplyWebPreferences(const WebPreferences& prefs, WebView* web_view) {
 #if defined(OS_ANDROID)
   settings->setAllowCustomScrollbarInMainFrame(false);
   settings->setTextAutosizingEnabled(prefs.text_autosizing_enabled);
-  settings->setTextAutosizingFontScaleFactor(prefs.font_scale_factor);
+  settings->setTextAutosizingFontScaleFactor(
+      prefs.font_scale_factor * GetFontScaleMultiplier(prefs));
   web_view->setIgnoreViewportTagScaleLimits(prefs.force_enable_zoom);
   settings->setAutoZoomFocusedNodeToLegibleScale(true);
   settings->setDoubleTapToZoomEnabled(prefs.double_tap_to_zoom_enabled);