Switch Linux CI to a docker image with freetype2.8

.taskcluster.yml

@@ -18,10 +18,12 @@ metadata:
 # instances configured and running.
 tasks:
   # For the docker-worker tasks, the Docker image used
-  # (staktrace/webrender-test:latest) was created using this Dockerfile:
+  # (staktrace/webrender-test:freetype28) was created using this Dockerfile:
   # ---
   #   FROM ubuntu:16.04
-  #   RUN apt-get -y update && apt-get install -y curl git python python-pip cmake pkg-config libx11-dev libgl1-mesa-dev libfontconfig1-dev
+  #   RUN apt-get -y update && apt-get install -y curl git python python-pip cmake pkg-config libx11-dev libgl1-mesa-dev libfontconfig1-dev software-properties-common
+  #   RUN add-apt-repository -y -u ppa:glasen/freetype2
+  #   RUN apt-get -y install freetype2-demos
   #   RUN pip install mako voluptuous PyYAML servo-tidy
   #   RUN useradd -d /home/worker -s /bin/bash -m worker
   #   USER worker
@@ -53,7 +55,7 @@ tasks:
           - master
     payload:
       maxRunTime: 3600
-      image: 'staktrace/webrender-test:latest'
+      image: 'staktrace/webrender-test:freetype28'
       env:
         RUST_BACKTRACE: 1
         RUSTFLAGS: '--deny warnings'
@@ -87,7 +89,7 @@ tasks:
           - master
     payload:
       maxRunTime: 3600
-      image: 'staktrace/webrender-test:latest'
+      image: 'staktrace/webrender-test:freetype28'
       env:
         RUST_BACKTRACE: 1
         RUSTFLAGS: '--deny warnings'