Makes the default ctor of gfx::FontList copy the pre-calculated metrics.

ui/gfx/font_list.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gfx/font_list.h"
 
 #include <algorithm>
 
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
 
 namespace {
 
 // Font description of the default font set.
 base::LazyInstance<std::string>::Leaky g_default_font_description =
     LAZY_INSTANCE_INITIALIZER;
 
+// The default instance of gfx::FontList, whose metrics are pre-calculated.
+// The default ctor of gfx::FontList copies the metrics so it won't need to
+// scan the whole font list to calculate the metrics.
+const gfx::FontList* g_default_font_list = NULL;
+
 // Parses font description into |font_names|, |font_style| and |font_size|.
 void ParseFontDescriptionString(const std::string& font_description_string,
                                 std::vector<std::string>* font_names,
                                 int* font_style,
                                 int* font_size) {
   base::SplitString(font_description_string, ',', font_names);
   DCHECK_GT(font_names->size(), 1U);
 
   // The last item is [STYLE_OPTIONS] SIZE.
   std::vector<std::string> styles_size;
@@ skipping 47 matching lines @@
 FontList::FontList()
     : common_height_(-1),
       common_baseline_(-1),
       font_style_(-1),
       font_size_(-1) {
   // SetDefaultFontDescription() must be called and the default font description
   // must be set earlier than any call of the default constructor.
   DCHECK(!(g_default_font_description == NULL))  // != is not overloaded.
       << "SetDefaultFontDescription has not been called.";
 
-  font_description_string_ = g_default_font_description.Get();
-  if (font_description_string_.empty())
-    fonts_.push_back(Font());
+  // Allocate the global instance of FontList for |g_default_font_list| without
+  // calling the default ctor.
+  static FontList default_font_list((Font()));
+
+  if (!g_default_font_list) {
+    default_font_list = g_default_font_description.Get().empty() ?
+        FontList(Font()) : FontList(g_default_font_description.Get());
+    // Pre-calculate the metrics.
+    if (default_font_list.GetPrimaryFont().platform_font()) {

[Alexei Svitkine (slow), 2014/01/09 20:58:13]

Can you add a comment explaining this if statement?

[Yuki, 2014/01/10 04:57:10]

Added a comment.

Android and Linux + Ozone don't support PlatformFont for now.  We cannot get any
font metrics on those platforms.

+      default_font_list.CacheCommonFontHeightAndBaseline();
+      default_font_list.CacheFontStyleAndSize();
+    }
+    g_default_font_list = &default_font_list;
+  }
+
+  // Copy the default font list specification and its pre-calculated metrics.
+  *this = *g_default_font_list;
 }
 
 FontList::FontList(const std::string& font_description_string)
     : font_description_string_(font_description_string),
       common_height_(-1),
       common_baseline_(-1),
       font_style_(-1),
       font_size_(-1) {
   DCHECK(!font_description_string.empty());
   // DCHECK description string ends with "px" for size in pixel.
@@ skipping 42 matching lines @@
 }
 
 // static
 void FontList::SetDefaultFontDescription(const std::string& font_description) {
   // The description string must end with "px" for size in pixel, or must be
   // the empty string, which specifies to use a single default font.
   DCHECK(font_description.empty() ||
          EndsWith(font_description, "px", true));
 
   g_default_font_description.Get() = font_description;
+  g_default_font_list = NULL;
 }
 
 FontList FontList::DeriveFontList(int font_style) const {
   return DeriveFontListWithSizeDeltaAndStyle(0, font_style);
 }
 
 FontList FontList::DeriveFontListWithSize(int size) const {
   DCHECK_GT(size, 0);
   return DeriveFontListWithSizeDeltaAndStyle(size - GetFontSize(),
                                              GetFontStyle());
@@ skipping 135 matching lines @@
     font_style_ = fonts_[0].GetStyle();
     font_size_ = fonts_[0].GetFontSize();
   } else {
     std::vector<std::string> font_names;
     ParseFontDescriptionString(font_description_string_, &font_names,
                                &font_style_, &font_size_);
   }
 }
 
 }  // namespace gfx