From 8daeeb159ae107906be59263995f00e474a3f77a Mon Sep 17 00:00:00 2001
From: Brian Birtles <birtles@gmail.com>
Date: Wed, 12 Jul 2017 08:49:10 +0900
Subject: [PATCH] Check Gecko pref before parsing frames() timing function

---
 components/style/gecko/generated/bindings.rs  |  3 +++
 .../style/values/specified/transform.rs       | 19 +++++++++++++++++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/components/style/gecko/generated/bindings.rs b/components/style/gecko/generated/bindings.rs
index 427992d8939..55c6b46474e 100644
--- a/components/style/gecko/generated/bindings.rs
+++ b/components/style/gecko/generated/bindings.rs
@@ -803,6 +803,9 @@ extern "C" {
                                           ComputedTimingFunction_BeforeFlag)
      -> f64;
 }
+extern "C" {
+    pub fn Gecko_IsFramesTimingEnabled() -> bool;
+}
 extern "C" {
     pub fn Gecko_AnimationGetBaseStyle(aBaseStyles:
                                            *mut ::std::os::raw::c_void,
diff --git a/components/style/values/specified/transform.rs b/components/style/values/specified/transform.rs
index 578a9b90ae3..e7af2e6b10f 100644
--- a/components/style/values/specified/transform.rs
+++ b/components/style/values/specified/transform.rs
@@ -131,6 +131,17 @@ impl<S> OriginComponent<S> {
     }
 }
 
+#[cfg(feature = "gecko")]
+#[inline]
+fn allow_frames_timing() -> bool {
+    use gecko_bindings::bindings;
+    unsafe { bindings::Gecko_IsFramesTimingEnabled() }
+}
+
+#[cfg(feature = "servo")]
+#[inline]
+fn allow_frames_timing() -> bool { true }
+
 impl Parse for TimingFunction {
     fn parse<'i, 't>(context: &ParserContext, input: &mut Parser<'i, 't>) -> Result<Self, ParseError<'i>> {
         if let Ok(keyword) = input.try(TimingKeyword::parse) {
@@ -172,8 +183,12 @@ impl Parse for TimingFunction {
                     Ok(GenericTimingFunction::Steps(steps, position))
                 },
                 "frames" => {
-                    let frames = Integer::parse_with_minimum(context, i, 2)?;
-                    Ok(GenericTimingFunction::Frames(frames))
+                    if allow_frames_timing() {
+                        let frames = Integer::parse_with_minimum(context, i, 2)?;
+                        Ok(GenericTimingFunction::Frames(frames))
+                    } else {
+                        Err(())
+                    }
                 },
                 _ => Err(()),
             }).map_err(|()| StyleParseError::UnexpectedFunction(function).into())