Fixed and reenabled the flaky test "WebViewAPITest.TestAutosizeAfterNavigation".

chrome/test/data/extensions/platform_apps/web_view/shim/main.js

Index: chrome/test/data/extensions/platform_apps/web_view/shim/main.js
diff --git a/chrome/test/data/extensions/platform_apps/web_view/shim/main.js b/chrome/test/data/extensions/platform_apps/web_view/shim/main.js
index 97dcc1a36fb0f0c71974879c26d534250119a7b4..91e7db85636620f7ad061c917fabad2c72d614f3 100644
--- a/chrome/test/data/extensions/platform_apps/web_view/shim/main.js
+++ b/chrome/test/data/extensions/platform_apps/web_view/shim/main.js
@@ -178,8 +178,9 @@ function testAutosizeBeforeNavigation() {
   webview.setAttribute('maxheight', 110);
 
   webview.addEventListener('sizechanged', function(e) {
-    embedder.test.assertEq(0, e.oldWidth);
-    embedder.test.assertEq(0, e.oldHeight);
+    // The old size should be the default size of the webview, which at the time
+    // of writing this comment is 300 x 300, but is not important to this test
+    // and could change in the future, so it is not checked here.
     embedder.test.assertTrue(e.newWidth >= 200 && e.newWidth <= 210);
     embedder.test.assertTrue(e.newHeight >= 100 && e.newHeight <= 110);
     embedder.test.succeed();