[Workaround] For running layout tests locally on Ubuntu16.04

content/shell/test_runner/resources/fonts/fonts.conf

Index: content/shell/test_runner/resources/fonts/fonts.conf
diff --git a/content/shell/test_runner/resources/fonts/fonts.conf b/content/shell/test_runner/resources/fonts/fonts.conf
index d337b12431d40127639bd7703d963f11d268412c..53eccb05c5844782ad7f546caeed0e195fd93455 100644
--- a/content/shell/test_runner/resources/fonts/fonts.conf
+++ b/content/shell/test_runner/resources/fonts/fonts.conf
@@ -249,4 +249,29 @@
     </edit>
   </match>
 
+  <!-- When we encounter a character that the current font doesn't
+       support, gfx::GetFallbackFontForChar() returns the first font
+       that does have a glyph for the character. The list of fonts is
+       sorted by a pattern that includes the current locale, but doesn't
+       include a font family (which means that the fallback font depends
+       on the locale but not on the current font).
+    
+       DejaVu Sans is commonly the only font that supports some
+       characters, such as "⇧", and even when other candidates are
+       available, DejaVu Sans is commonly first among them, because of
+       the way Fontconfig is ordinarily configured. For example, the
+       configuration in the Fonconfig source lists DejaVu Sans under the
+       sans-serif generic family, and appends sans-serif to patterns
+       that don't already include a generic family (such as the pattern
+       in gfx::GetFallbackFontForChar()).
+    
+       To get the same fallback font in the layout tests, we could
+       duplicate this configuration here, or more directly, simply
+       append DejaVu Sans to all patterns. -->
+  <match target="pattern">
+    <edit name="family" mode="append_last">
+      <string>DejaVu Sans</string>
+    </edit>
+  </match>
+
 </fontconfig>