Add WebRender to cargotest

src/ci/docker/x86_64-gnu-cargotest/Dockerfile

@@ -12,7 +12,11 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
   libssl-dev \
   sudo \
   xz-utils \
-  pkg-config
+  pkg-config \
+  libgl1-mesa-dev \
+  llvm-dev \
+  libfreetype6-dev \
+  libexpat1-dev
 
 COPY scripts/sccache.sh /scripts/
 RUN sh /scripts/sccache.sh

src/tools/cargotest/main.rs

@@ -67,6 +67,13 @@ const TEST_REPOS: &'static [Test] = &[
         // This takes much less time to build than all of Servo and supports stable Rust.
         packages: &["stylo_tests", "selectors"],
     },
+    Test {
+        name: "webrender",
+        repo: "https://github.com/servo/webrender",
+        sha: "57250b2b8fa63934f80e5376a29f7dcb3f759ad6",
+        lock: None,
+        packages: &[],
+    },
 ];
 
 fn main() {