Bug 1461858 part 2 - Make from_image_request infallible. r=emilio

All callsites already assert, so moving the assertion into the method
should be fine. It is not expected to handle a null image value anyway.

MozReview-Commit-ID: J8CA8m22eSv

--HG--
extra : rebase_source : e4d524263363393d3d0388ede8efcae096917546

servo/components/style/gecko/url.rs

@@ -317,13 +317,10 @@ impl ComputedImageUrl {
     }
 
     /// Convert from nsStyleImageReques to ComputedImageUrl.
-    pub unsafe fn from_image_request(image_request: &nsStyleImageRequest) -> Result<Self, ()> {
+    pub unsafe fn from_image_request(image_request: &nsStyleImageRequest) -> Self {
-        if image_request.mImageValue.mRawPtr.is_null() {
+        let image_value = image_request.mImageValue.mRawPtr
-            return Err(());
+            .as_ref().expect("mImageValue is null");
-        }
-
-        let image_value = image_request.mImageValue.mRawPtr.as_ref().unwrap();
         let url_value_data = &image_value._base;
-        Ok(Self::from_url_value_data(url_value_data))
+        Self::from_url_value_data(url_value_data)
     }
 }

servo/components/style/properties/gecko.mako.rs

@@ -4145,9 +4145,7 @@ fn static_assert() {
 
         unsafe {
             let ref gecko_image_request = *self.gecko.mListStyleImage.mRawPtr;
-            UrlOrNone::Url(ComputedImageUrl::from_image_request(
+            UrlOrNone::Url(ComputedImageUrl::from_image_request(gecko_image_request))
-                gecko_image_request
-            ).expect("mListStyleImage could not convert to ComputedImageUrl"))
         }
     }
 
@@ -5437,7 +5435,6 @@ clip-path
             let url = unsafe {
                 let gecko_image_request = gecko_cursor_image.mImage.mRawPtr.as_ref().unwrap();
                 ComputedImageUrl::from_image_request(&gecko_image_request)
-                    .expect("mCursorImages.mImage could not convert to ComputedImageUrl")
             };
 
             let hotspot =
@@ -5713,7 +5710,6 @@ clip-path
                                 &**gecko_content.mContent.mImage.as_ref();
                             ContentItem::Url(
                                 ComputedImageUrl::from_image_request(gecko_image_request)
-                                    .expect("mContent could not convert to ComputedImageUrl")
                             )
                         }
                     },