Add a runtime-wide initialization hook for Geckolib.

ports/geckolib/bindings.rs

@@ -104,6 +104,7 @@ extern "C" {
      -> *const u16;
     pub fn Gecko_Namespace(element: *mut RawGeckoElement, length: *mut u32)
      -> *const u16;
+    pub fn Servo_Initialize();
     pub fn Servo_RestyleDocument(doc: *mut RawGeckoDocument,
                                  set: *mut RawServoStyleSet);
     pub fn Gecko_Construct_nsStyleFont(ptr: *mut nsStyleFont);

ports/geckolib/glue.rs

@@ -61,6 +61,10 @@ pub fn pseudo_element_from_atom(pseudo: *mut nsIAtom,
  * depend on but good enough for our purposes.
  */
 
+#[no_mangle]
+pub extern "C" fn Servo_Initialize() -> () {
+}
+
 #[no_mangle]
 pub extern "C" fn Servo_RestyleDocument(doc: *mut RawGeckoDocument, raw_data: *mut RawServoStyleSet) -> () {
     let document = unsafe { GeckoDocument::from_raw(doc) };
@@ -71,8 +75,12 @@ pub extern "C" fn Servo_RestyleDocument(doc: *mut RawGeckoDocument, raw_data: *m
     let data = unsafe { &mut *(raw_data as *mut PerDocumentStyleData) };
 
     // Force the creation of our lazily-constructed initial computed values on
-    // the main thread, since it's not safe to call elsewhere. This should move
+    // the main thread, since it's not safe to call elsewhere.
-    // into a runtime-wide init hook at some point.
+    //
+    // FIXME(bholley): this should move into Servo_Initialize as soon as we get
+    // rid of the HackilyFindSomeDeviceContext stuff that happens during
+    // initial_values computation, since that stuff needs to be called further
+    // along in startup than the sensible place to call Servo_Initialize.
     GeckoComputedValues::initial_values();
 
     let _needs_dirtying = Arc::get_mut(&mut data.stylist).unwrap()