Disable FrameNavigationEntry_NewSubframe on Linux due to flakes.

content/browser/frame_host/navigation_controller_impl_browsertest.cc

Index: content/browser/frame_host/navigation_controller_impl_browsertest.cc
diff --git a/content/browser/frame_host/navigation_controller_impl_browsertest.cc b/content/browser/frame_host/navigation_controller_impl_browsertest.cc
index 4b8b1573f55143cc41551c3cc1545c8d863b947d..85afbdb2bea4c574c8b00ece48cf6f5c22954d1a 100644
--- a/content/browser/frame_host/navigation_controller_impl_browsertest.cc
+++ b/content/browser/frame_host/navigation_controller_impl_browsertest.cc
@@ -2259,8 +2259,15 @@ IN_PROC_BROWSER_TEST_F(NavigationControllerBrowserTest,
 
 // Verify the tree of FrameNavigationEntries after NAVIGATION_TYPE_NEW_SUBFRAME
 // commits.
+// Disabled due to flakes on Linux Tests; see https://crbug.com/646836.
+#if defined(OS_LINUX)
+#define MAYBE_FrameNavigationEntry_NewSubframe \
+    DISABLED_FrameNavigationEntry_NewSubframe
+#else
+#define MAYBE_FrameNavigationEntry_NewSubframe FrameNavigationEntry_NewSubframe
+#endif
 IN_PROC_BROWSER_TEST_F(NavigationControllerBrowserTest,
-                       FrameNavigationEntry_NewSubframe) {
+                       MAYBE_FrameNavigationEntry_NewSubframe) {
   GURL main_url(embedded_test_server()->GetURL(
       "/navigation_controller/simple_page_1.html"));
   NavigateToURL(shell(), main_url);