Auto merge of #12076 - jdm:font-load, r=pcwalton

Make font template data load fallible

Remove a TODO around dealing with a failed file operation.

Can we write an automated test for this? I don't really know what font template data is, but this failure seems to be fontconfig-specific...

---
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #12037
- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="35" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/12076)
<!-- Reviewable:end -->

components/gfx/platform/freetype/font_template.rs

@@ -3,7 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use std::fs::File;
-use std::io::Read;
+use std::io::{Read, Error};
 use string_cache::Atom;
 use webrender_traits::NativeFontHandle;
 
@@ -18,24 +18,24 @@ pub struct FontTemplateData {
 }
 
 impl FontTemplateData {
-    pub fn new(identifier: Atom, font_data: Option<Vec<u8>>) -> FontTemplateData {
+    pub fn new(identifier: Atom, font_data: Option<Vec<u8>>) -> Result<FontTemplateData, Error> {
         let bytes = match font_data {
             Some(bytes) => {
                 bytes
             },
             None => {
                 // TODO: Handle file load failure!
-                let mut file = File::open(&*identifier).unwrap();
+                let mut file = try!(File::open(&*identifier));
                 let mut buffer = vec![];
                 file.read_to_end(&mut buffer).unwrap();
                 buffer
             },
         };
 
-        FontTemplateData {
+        Ok(FontTemplateData {
             bytes: bytes,
             identifier: identifier,
-        }
+        })
     }
 
     /// Returns a clone of the data in this font. This may be a hugely expensive

components/gfx/platform/macos/font_template.rs

@@ -12,7 +12,7 @@ use serde::de::{Error, Visitor};
 use std::borrow::ToOwned;
 use std::collections::HashMap;
 use std::fs::File;
-use std::io::Read;
+use std::io::{Read, Error as IoError};
 use std::ops::Deref;
 use std::sync::Mutex;
 use string_cache::Atom;
@@ -41,12 +41,12 @@ unsafe impl Send for FontTemplateData {}
 unsafe impl Sync for FontTemplateData {}
 
 impl FontTemplateData {
-    pub fn new(identifier: Atom, font_data: Option<Vec<u8>>) -> FontTemplateData {
-        FontTemplateData {
+    pub fn new(identifier: Atom, font_data: Option<Vec<u8>>) -> Result<FontTemplateData, IoError> {
+        Ok(FontTemplateData {
             ctfont: CachedCTFont(Mutex::new(HashMap::new())),
             identifier: identifier.to_owned(),
             font_data: font_data
-        }
+        })
     }
 
     /// Retrieves the Core Text font instance, instantiating it if necessary.