Auto merge of #12395 - jdm:nowrap, r=Ms2ger

Avoid calling JS_WrapValue for same-compartment DOM reflectors

This change shaves off 15-20ns per iteration of the node.firstChild getter test in tests/html/bindings_perf.html. Based on [similar Gecko code](http://searchfox.org/mozilla-central/rev/f43c9e0ffa92e72dbdbcbf57eecf04a43d46da63/dom/bindings/BindingUtils.h#781).

---
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix (partially) #12358

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2 files changed, 17 insertions, 12 deletions

diff --git a/components/script/dom/bindings/codegen/CodegenRust.py b/components/script/dom/bindings/codegen/CodegenRust.py
index 8c0d27afb82..2513b5b92eb 100644
--- a/components/script/dom/bindings/codegen/CodegenRust.py
+++ b/components/script/dom/bindings/codegen/CodegenRust.py
@@ -5533,17 +5533,17 @@ class CGBindingRoot(CGThing):
             'js::jsapi::{JSJitInfo_AliasSet, JSJitInfo_ArgType, AutoIdVector, CallArgs, FreeOp}',
             'js::jsapi::{JSITER_SYMBOLS, JSPROP_ENUMERATE, JSPROP_PERMANENT, JSPROP_READONLY, JSPROP_SHARED}',
             'js::jsapi::{JSCLASS_RESERVED_SLOTS_SHIFT, JSITER_HIDDEN, JSITER_OWNONLY}',
-            'js::jsapi::{GetGlobalForObjectCrossCompartment , GetPropertyKeys, Handle}',
+            'js::jsapi::{GetPropertyKeys, Handle}',
             'js::jsapi::{HandleId, HandleObject, HandleValue, HandleValueArray}',
             'js::jsapi::{INTERNED_STRING_TO_JSID, IsCallable, JS_CallFunctionValue}',
-            'js::jsapi::{JS_ComputeThis, JS_CopyPropertiesFrom, JS_ForwardGetPropertyTo}',
+            'js::jsapi::{JS_CopyPropertiesFrom, JS_ForwardGetPropertyTo}',
             'js::jsapi::{JS_GetClass, JS_GetErrorPrototype, JS_GetFunctionPrototype}',
             'js::jsapi::{JS_GetGlobalForObject, JS_GetObjectPrototype, JS_GetProperty}',
             'js::jsapi::{JS_GetPropertyById, JS_GetPropertyDescriptorById, JS_GetReservedSlot}',
             'js::jsapi::{JS_HasProperty, JS_HasPropertyById, JS_InitializePropertiesFromCompatibleNativeObject}',
-            'js::jsapi::{JS_AtomizeAndPinString, JS_IsExceptionPending, JS_NewObject, JS_NewObjectWithGivenProto}',
-            'js::jsapi::{JS_NewObjectWithoutMetadata, JS_NewStringCopyZ, JS_SetProperty}',
-            'js::jsapi::{JS_SetPrototype, JS_SetReservedSlot, JS_WrapValue, JSAutoCompartment}',
+            'js::jsapi::{JS_AtomizeAndPinString, JS_NewObject, JS_NewObjectWithGivenProto}',
+            'js::jsapi::{JS_NewObjectWithoutMetadata, JS_SetProperty}',
+            'js::jsapi::{JS_SetPrototype, JS_SetReservedSlot, JSAutoCompartment}',
             'js::jsapi::{JSContext, JSClass, JSFreeOp, JSFunctionSpec}',
             'js::jsapi::{JSJitGetterCallArgs, JSJitInfo, JSJitMethodCallArgs, JSJitSetterCallArgs}',
             'js::jsapi::{JSNative, JSObject, JSNativeWrapper, JSPropertySpec}',
@@ -5556,8 +5556,7 @@ class CGBindingRoot(CGThing):
             'js::jsval::{NullValue, UndefinedValue}',
             'js::glue::{CallJitMethodOp, CallJitGetterOp, CallJitSetterOp, CreateProxyHandler}',
             'js::glue::{GetProxyPrivate, NewProxyObject, ProxyTraps}',
-            'js::glue::{RUST_FUNCTION_VALUE_TO_JITINFO}',
-            'js::glue::{RUST_JS_NumberValue, RUST_JSID_IS_STRING, int_to_jsid}',
+            'js::glue::{RUST_JSID_IS_STRING, int_to_jsid}',
             'js::glue::AppendToAutoIdVector',
             'js::rust::{GCMethods, define_methods, define_properties}',
             'dom::bindings',
diff --git a/components/script/dom/bindings/conversions.rs b/components/script/dom/bindings/conversions.rs
index 80911b65e74..01282ea3b1f 100644
--- a/components/script/dom/bindings/conversions.rs
+++ b/components/script/dom/bindings/conversions.rs
@@ -47,9 +47,9 @@ use js::glue::{RUST_JSID_IS_STRING, RUST_JSID_TO_STRING, UnwrapObject};
 use js::jsapi::{HandleId, HandleObject, HandleValue, JSClass, JSContext};
 use js::jsapi::{JSObject, JSString, JS_GetArrayBufferViewType, JS_GetClass};
 use js::jsapi::{JS_GetLatin1StringCharsAndLength, JS_GetObjectAsArrayBufferView};
-use js::jsapi::{JS_GetReservedSlot, JS_GetTwoByteStringCharsAndLength};
+use js::jsapi::{JS_GetReservedSlot, JS_GetTwoByteStringCharsAndLength, ToWindowProxyIfWindow};
 use js::jsapi::{JS_IsArrayObject, JS_NewStringCopyN, JS_StringHasLatin1Chars};
-use js::jsapi::{JS_WrapValue, MutableHandleValue, Type};
+use js::jsapi::{JS_WrapValue, MutableHandleValue, Type, IsObjectInContextCompartment};
 use js::jsval::{ObjectValue, StringValue};
 use js::rust::ToString;
 use libc;
@@ -276,9 +276,15 @@ impl ToJSValConvertible for Reflector {
     unsafe fn to_jsval(&self, cx: *mut JSContext, rval: MutableHandleValue) {
         let obj = self.get_jsobject().get();
         assert!(!obj.is_null());
-        rval.set(ObjectValue(&*obj));
-        if !JS_WrapValue(cx, rval) {
-            panic!("JS_WrapValue failed.");
+        let same_compartment = IsObjectInContextCompartment(obj, cx);
+        if same_compartment {
+            rval.set(ObjectValue(&*ToWindowProxyIfWindow(obj)));
+        } else {
+            rval.set(ObjectValue(&*obj));
+
+            if !JS_WrapValue(cx, rval) {
+                panic!("JS_WrapValue failed.");
+            }
         }
     }
 }