linux: Cache GetFontRenderParams() results.

ui/gfx/font_render_params.h

 // Copyright 2014 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.
 
 #ifndef UI_GFX_FONT_RENDER_PARAMS_H_
 #define UI_GFX_FONT_RENDER_PARAMS_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 73 matching lines @@
   int style;
 };
 
 // Returns the appropriate parameters for rendering the font described by
 // |query|. If |family_out| is non-NULL, it will be updated to contain the
 // recommended font family from |query.families|.
 GFX_EXPORT FontRenderParams GetFontRenderParams(
     const FontRenderParamsQuery& query,
     std::string* family_out);
 
+// Clears GetFontRenderParams()'s cache. Intended to be called by tests that are
+// changing Fontconfig's configuration.
+// TODO(derat): This is only defined for Linux, but OS_LINUX doesn't seem to be
+// set when font_render_params_linux_unittest.cc includes this header. Figure
+// out what's going on here.
+GFX_EXPORT void ClearFontRenderParamsCacheForTest();
+
 }  // namespace gfx
 
 #endif  // UI_GFX_FONT_RENDER_PARAMS_H_