Don't resolve URLs at parse time for Stylo.

It's a bit unfortunate the use separate implementations of SpecifiedUrl for Servo
and Gecko, but they're different enough at this point that I don't think it really
makes sense to try to share everything. Splitting them out has some nice
simplifications as well.

I recognize that there's still some potential correctness issues for Servo using
the resolved URI in various places where the original URI may be the right thing,
but I've got too much on my plate to look into that for now.

MozReview-Commit-ID: BeDu93TQ4Ow

components/style/gecko/url.rs

@@ -0,0 +1,104 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Common handling for the specified value CSS url() values.
+
+use cssparser::CssStringWriter;
+use gecko_bindings::structs::ServoBundledURI;
+use gecko_bindings::sugar::refptr::{GeckoArcPrincipal, GeckoArcURI};
+use parser::ParserContext;
+use std::borrow::Cow;
+use std::fmt::{self, Write};
+use std::sync::Arc;
+use style_traits::ToCss;
+
+/// A specified url() value for gecko. Gecko does not eagerly resolve SpecifiedUrls.
+#[derive(Clone, Debug, PartialEq)]
+pub struct SpecifiedUrl {
+    /// The URL in unresolved string form.
+    ///
+    /// Refcounted since cloning this should be cheap and data: uris can be
+    /// really large.
+    serialization: Arc<String>,
+
+    /// The base URI.
+    pub base: GeckoArcURI,
+    /// The referrer.
+    pub referrer: GeckoArcURI,
+    /// The principal that originated this URI.
+    pub principal: GeckoArcPrincipal,
+}
+
+impl SpecifiedUrl {
+    /// Try to parse a URL from a string value that is a valid CSS token for a
+    /// URL.
+    ///
+    /// Returns `Err` in the case that extra_data is incomplete.
+    pub fn parse_from_string<'a>(url: Cow<'a, str>,
+                                 context: &ParserContext)
+                                 -> Result<Self, ()> {
+        let extra = &context.extra_data;
+        if extra.base.is_none() || extra.referrer.is_none() || extra.principal.is_none() {
+            // FIXME(heycam) should ensure we always have a principal, etc.,
+            // when parsing style attributes and re-parsing due to CSS
+            // Variables.
+            warn!("stylo: skipping declaration without ParserContextExtraData");
+            return Err(())
+        }
+
+        Ok(SpecifiedUrl {
+            serialization: Arc::new(url.into_owned()),
+            base: extra.base.as_ref().unwrap().clone(),
+            referrer: extra.referrer.as_ref().unwrap().clone(),
+            principal: extra.principal.as_ref().unwrap().clone(),
+        })
+    }
+
+    /// Returns true if the URL is definitely invalid. We don't eagerly resolve
+    /// URLs in gecko, so we just return false here.
+    /// use its |resolved| status.
+    pub fn is_invalid(&self) -> bool {
+        false
+    }
+
+    /// Returns true if this URL looks like a fragment.
+    /// See https://drafts.csswg.org/css-values/#local-urls
+    pub fn is_fragment(&self) -> bool {
+        self.as_str().chars().next().map_or(false, |c| c == '#')
+    }
+
+    /// Return the resolved url as string, or the empty string if it's invalid.
+    ///
+    /// FIXME(bholley): This returns the unresolved URL while the servo version
+    /// returns the resolved URL.
+    pub fn as_str(&self) -> &str {
+        &*self.serialization
+    }
+
+    /// Little helper for Gecko's ffi.
+    pub fn as_slice_components(&self) -> (*const u8, usize) {
+        (self.serialization.as_str().as_ptr(), self.serialization.as_str().len())
+    }
+
+    /// Create a bundled URI suitable for sending to Gecko
+    /// to be constructed into a css::URLValue
+    pub fn for_ffi(&self) -> ServoBundledURI {
+        let (ptr, len) = self.as_slice_components();
+        ServoBundledURI {
+            mURLString: ptr,
+            mURLStringLength: len as u32,
+            mBaseURI: self.base.get(),
+            mReferrer: self.referrer.get(),
+            mPrincipal: self.principal.get(),
+        }
+    }
+}
+
+impl ToCss for SpecifiedUrl {
+    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+        try!(dest.write_str("url(\""));
+        try!(CssStringWriter::new(dest).write_str(&*self.serialization));
+        dest.write_str("\")")
+    }
+}