Don't crash when using IME on an input field with a CSS-specified font.

content/common/mac/attributed_string_coder.mm

Index: content/common/mac/attributed_string_coder.mm
diff --git a/content/common/mac/attributed_string_coder.mm b/content/common/mac/attributed_string_coder.mm
index bcd8b118c5543ee773bab42063fc2d19a2416d61..ed377bb91d1374045be73e6548d2b256be3c31b9 100644
--- a/content/common/mac/attributed_string_coder.mm
+++ b/content/common/mac/attributed_string_coder.mm
@@ -100,10 +100,12 @@ AttributedStringCoder::FontAttribute::FontAttribute()
 AttributedStringCoder::FontAttribute::~FontAttribute() {
 }
 
-NSDictionary* AttributedStringCoder::FontAttribute::ToAttributesDictionary(
-    void) const {
+NSDictionary*
+AttributedStringCoder::FontAttribute::ToAttributesDictionary() const {
   DCHECK(ShouldEncode());
   NSFont* font = font_descriptor_.ToNSFont();
+  if (!font)
+    return [NSDictionary dictionary];
   return [NSDictionary dictionaryWithObject:font forKey:NSFontAttributeName];
 }