Unprefix -webkit-filter and add a pixel test for it.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/850103003

engine/src/flutter/HACKING.md

@@ -54,7 +54,8 @@ uploaded file in the reference.
 2. Create an dummy reference file (foo-expected.sky).
 3. Run the test (it will fail).
 4. Copy the -actual.png file to googlestorage (see below).
-5. Put an <img> pointing to your newly uploaded png in the reference file.
+5. Put an <img> pointing to your newly uploaded png in the reference file at
+http://storage.googleapis.com/mojo/sky-pngs/SHA1_HASH_HERE
 
 Copying the file to googlestorage:
 $ sha1sum ../out/Debug/layout-test-results/framework/flights-app-pixels-actual.png

engine/src/flutter/tests/lowlevel/filters-expected.sky

@@ -0,0 +1,13 @@
+<foo>
+<import src="../resources/run-after-display.sky" as="runAfterDisplay" />
+
+<img src="http://storage.googleapis.com/mojo/sky-pngs/9a7b59f74e2bbcd0d0ceee17ead05b0da64a2af7" />
+
+<script>
+window.addEventListener('load', function() {
+  runAfterDisplay(function() {
+    internals.notifyTestComplete("");
+  });
+});
+</script>
+</foo>

engine/src/flutter/tests/lowlevel/filters.sky

@@ -0,0 +1,11 @@
+<foo>
+<import src="../resources/run-after-display.sky" as="runAfterDisplay" />
+
+<div style="filter: grayscale(1) blur(2px); color: green;">This should be gray and blurred</div>
+
+<script>
+runAfterDisplay(function() {
+    internals.notifyTestComplete("");
+});
+</script>
+</foo>