Disable flaky test.

Had previously been re-enabled but appears to be flaking more
frequently again.

Bug: 1126876
Change-Id: Id3a6c5d50bb031b09646f9dddb6c5f5fe1960213
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2645466
Commit-Queue: Katie Dektar <katie@chromium.org>
Commit-Queue: Daniel Hosseinian <dhoss@chromium.org>
Auto-Submit: Katie Dektar <katie@chromium.org>
Reviewed-by: Hui Yingst <nigi@chromium.org>
Reviewed-by: Daniel Hosseinian <dhoss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#846363}

chrome/browser/pdf/pdf_extension_test.cc

@@ -490,10 +490,16 @@ IN_PROC_BROWSER_TEST_F(PDFExtensionTestWithTestGuestViewManager,
 // has the correct URL for the PDF extension.
 // TODO(wjmaclean): Are there any attributes we can/should test with respect to
 // the extension's loaded html?
-// TODO(https://crbug.com/1034972): Re-enable. Flaky on all platforms.
-// Temporarily re-enabling on all platforms to collect diagnostic data.
+// TODO(https://crbug.com/1126876): Re-enable. Flaky on all linux, chromeos and
+// windows.
+#if defined(OS_WIN) || defined(OS_LINUX) || BUILDFLAG(IS_CHROMEOS_ASH) || \
+    BUILDFLAG(IS_CHROMEOS_LACROS)
+#define MAYBE_PdfExtensionLoadedInGuest DISABLED_PdfExtensionLoadedInGuest
+#else
+#define MAYBE_PdfExtensionLoadedInGuest PdfExtensionLoadedInGuest
+#endif
 IN_PROC_BROWSER_TEST_F(PDFExtensionTestWithTestGuestViewManager,
-                       PdfExtensionLoadedInGuest) {
+                       MAYBE_PdfExtensionLoadedInGuest) {
   // Load test HTML, and verify the text area has focus.
   GURL main_url(embedded_test_server()->GetURL("/pdf/test.pdf"));
   ui_test_utils::NavigateToURL(browser(), main_url);