Update WR (pixel snapping improvements).

This includes a WR update that improves pixel snapping. Specifically,
the non-transform shader now snaps to device pixels in world space,
rather than local space.

This makes 31 new tests pass, and adds 4 new failures.

Of the new failures:
 - The three background size tests appear to be an OSMesa accuracy
   issue. Near the bottom of the image, a small number of pixels
   are different from the reference by a value of 1.0 / 255.0. I've
   confirmed on 3 real GPUs and also on llvmpipe that the tests
   match on those devices. This would be a good case for fuzzy test
   support in WPT.
 - The other failing test appears to have unreasonable accuracy
   requirements as it also fails on Gecko and Chromium in the same
   way that the test now fails on WR.

tests/wpt/metadata-css/css-transforms-1_dev/html/css-transforms-3d-on-anonymous-block-001.htm.ini

@@ -1,4 +0,0 @@
-[css-transforms-3d-on-anonymous-block-001.htm]
-  type: reftest
-  expected:
-    if os == "linux": FAIL

tests/wpt/metadata-css/css-transforms-1_dev/html/rotate_x_45deg.htm.ini

@@ -1,3 +1,4 @@
 [rotate_x_45deg.htm]
   type: reftest
-  expected: FAIL
+  expected:
+    if os == "linux": FAIL

tests/wpt/metadata-css/css-transforms-1_dev/html/transform-input-014.htm.ini

@@ -1,4 +0,0 @@
-[transform-input-014.htm]
-  type: reftest
-  expected:
-    if os == "mac": FAIL

tests/wpt/metadata-css/css-transforms-1_dev/html/transform-input-015.htm.ini

@@ -1,4 +0,0 @@
-[transform-input-015.htm]
-  type: reftest
-  expected:
-    if os == "mac": FAIL

tests/wpt/metadata-css/css-transforms-1_dev/html/transform-input-017.htm.ini

@@ -1,4 +0,0 @@
-[transform-input-017.htm]
-  type: reftest
-  expected:
-    if os == "linux": FAIL

tests/wpt/metadata-css/css-transforms-1_dev/html/transform-input-018.htm.ini

@@ -1,4 +0,0 @@
-[transform-input-018.htm]
-  type: reftest
-  expected:
-    if os == "linux": FAIL

tests/wpt/metadata-css/css-transforms-1_dev/html/transform-input-019.htm.ini

@@ -1,3 +0,0 @@
-[transform-input-019.htm]
-  type: reftest
-  expected: FAIL