style: Add ToShmem impl for UrlExtraData.

Differential Revision: https://phabricator.services.mozilla.com/D17195

components/style/stylesheets/mod.rs

@@ -37,8 +37,9 @@ use malloc_size_of::{MallocSizeOfOps, MallocUnconditionalShallowSizeOf};
 use servo_arc::Arc;
 use std::fmt;
 #[cfg(feature = "gecko")]
-use std::mem;
+use std::mem::{self, ManuallyDrop};
 use style_traits::ParsingMode;
+use to_shmem::{SharedMemoryBuilder, ToShmem};
 
 pub use self::counter_style_rule::CounterStyleRule;
 pub use self::document_rule::DocumentRule;
@@ -101,6 +102,26 @@ impl Drop for UrlExtraData {
     }
 }
 
+#[cfg(feature = "gecko")]
+impl ToShmem for UrlExtraData {
+    fn to_shmem(&self, _builder: &mut SharedMemoryBuilder) -> ManuallyDrop<Self> {
+        if self.0 & 1 == 0 {
+            let shared_extra_datas = unsafe { &structs::URLExtraData_sShared };
+            let self_ptr = self.as_ref() as *const _ as *mut _;
+            let sheet_id = shared_extra_datas
+                .iter()
+                .position(|r| r.mRawPtr == self_ptr)
+                .expect(
+                    "ToShmem failed for UrlExtraData: expected sheet's URLExtraData to be in \
+                     URLExtraData::sShared",
+                );
+            ManuallyDrop::new(UrlExtraData((sheet_id << 1) | 1))
+        } else {
+            ManuallyDrop::new(UrlExtraData(self.0))
+        }
+    }
+}
+
 #[cfg(feature = "gecko")]
 impl UrlExtraData {
     /// Create a new UrlExtraData wrapping a pointer to the specified Gecko