Make `getComputedStyle` return the correct style for collapsed <img> elements.

third_party/WebKit/LayoutTests/http/tests/subresource_filter/image-allow-disallow-transitions.html

Index: third_party/WebKit/LayoutTests/http/tests/subresource_filter/image-allow-disallow-transitions.html
diff --git a/third_party/WebKit/LayoutTests/http/tests/subresource_filter/image-allow-disallow-transitions.html b/third_party/WebKit/LayoutTests/http/tests/subresource_filter/image-allow-disallow-transitions.html
index 168c1e9e318cf6ee4a0dfaf3aaafa60c039ce1ec..46d26cf8274ccad341b05a4e647737f74eb06649 100644
--- a/third_party/WebKit/LayoutTests/http/tests/subresource_filter/image-allow-disallow-transitions.html
+++ b/third_party/WebKit/LayoutTests/http/tests/subresource_filter/image-allow-disallow-transitions.html
@@ -37,6 +37,12 @@ var EXPECTED_WIDTH = {
   "collapsed": 0
 };
 
+var EXPECTED_DISPLAY = {
+  "primary": "inline",
+  "fallback": "inline",
+  "collapsed": "none",
+};
+
 var numPendingImages =
     Object.keys(INITIAL_URLS).length * Object.keys(FINAL_URLS).length;
 
@@ -68,8 +74,11 @@ for (let [initialState, initialUrl] of Object.entries(INITIAL_URLS)) {
         .then(t.step_func_done(_ => {
           assert_equals(img.clientWidth, EXPECTED_WIDTH[finalState],
               "Image has incorrect width for the expected final state.");
+          let style = window.getComputedStyle(img);
+          assert_equals(style.display, EXPECTED_DISPLAY[finalState],
+              "Images has incorrect computed style for the final state.");
         }));
-    }, "State transition " + initialState + " to " + finalState);
+    }, "State transition " + initialState + " to " + finalState + ". ");
     cell.append(img);
   }
 }