The mathml/opentype/opentype-stretchy-horizontal.html layout test is flaky on WPE. You toss a coin, and the test result follows.

--- /app/webkit/WebKitBuild/Release/layout-test-results/mathml/opentype/opentype-stretchy-horizontal-expected.txt
+++ /app/webkit/WebKitBuild/Release/layout-test-results/mathml/opentype/opentype-stretchy-horizontal-actual.txt
@@ -1,33 +1,33 @@
 layer at (0,0) size 800x600
   RenderView at (0,0) size 800x600
-layer at (0,0) size 800x156
-  RenderBlock {HTML} at (0,0) size 800x156
-    RenderBody {BODY} at (8,16) size 784x124
-      RenderBlock {P} at (0,0) size 784x25
-        RenderMathMLMath {math} at (0,2) size 10x23
-          RenderMathMLRow {mstyle} at (0,0) size 10x23
-            RenderMathMLUnderOver {mover} at (0,0) size 10x23
-              RenderMathMLOperator {mo} at (0,1) size 10x22
+layer at (0,0) size 800x118
+  RenderBlock {HTML} at (0,0) size 800x118
+    RenderBody {BODY} at (8,16) size 784x86
+      RenderBlock {P} at (0,0) size 784x18
+        RenderMathMLMath {math} at (0,12) size 8x4
+          RenderMathMLRow {mstyle} at (0,0) size 8x4
+            RenderMathMLUnderOver {mover} at (0,0) size 8x4
+              RenderMathMLOperator {mo} at (3,1) size 2x3
                 RenderBlock (anonymous) at (0,0) size 1x3
                   RenderText {#text} at (0,-4) size 1x0
                     text run at (0,-4) width 1: "\x{219C}"
-              RenderMathMLSpace {mspace} at (1,0) size 8x1
+              RenderMathMLSpace {mspace} at (0,0) size 8x1
         RenderText {#text} at (0,0) size 0x0
-      RenderBlock {P} at (0,41) size 784x24
-        RenderMathMLMath {math} at (0,2) size 20x22
-          RenderMathMLRow {mstyle} at (0,0) size 20x22
-            RenderMathMLUnderOver {mover} at (0,0) size 20x22
-              RenderMathMLOperator {mo} at (0,1) size 20x21
+      RenderBlock {P} at (0,34) size 784x18
+        RenderMathMLMath {math} at (0,12) size 15x4
+          RenderMathMLRow {mstyle} at (0,0) size 15x4
+            RenderMathMLUnderOver {mover} at (0,0) size 15x4
+              RenderMathMLOperator {mo} at (7,1) size 1x3
                 RenderBlock (anonymous) at (0,0) size 1x3
                   RenderText {#text} at (0,-4) size 1x0
                     text run at (0,-4) width 1: "\x{219C}"
-              RenderMathMLSpace {mspace} at (2,0) size 16x1
+              RenderMathMLSpace {mspace} at (0,0) size 15x1
         RenderText {#text} at (0,0) size 0x0
-      RenderBlock {P} at (0,81) size 784x43
-        RenderMathMLMath {math} at (0,0) size 150x43
-          RenderMathMLRow {mstyle} at (0,0) size 150x43
-            RenderMathMLUnderOver {mover} at (0,0) size 150x43
-              RenderMathMLOperator {mo} at (0,1) size 150x42
+      RenderBlock {P} at (0,68) size 784x18
+        RenderMathMLMath {math} at (0,12) size 150x4
+          RenderMathMLRow {mstyle} at (0,0) size 150x4
+            RenderMathMLUnderOver {mover} at (0,0) size 150x4
+              RenderMathMLOperator {mo} at (74,1) size 2x3
                 RenderBlock (anonymous) at (0,0) size 1x3
                   RenderText {#text} at (0,-4) size 1x0
                     text run at (0,-4) width 1: "\x{219C}"