Disable WebViewTest.Shim_TestNestedSubframes on Mac.

chrome/browser/apps/guest_view/web_view_browsertest.cc

Index: chrome/browser/apps/guest_view/web_view_browsertest.cc
diff --git a/chrome/browser/apps/guest_view/web_view_browsertest.cc b/chrome/browser/apps/guest_view/web_view_browsertest.cc
index cf2b44733cec8d9509ae0a8290c486cb5dc0c224..4ede1058fe77f4e98aa117a74979384c30c0a8bf 100644
--- a/chrome/browser/apps/guest_view/web_view_browsertest.cc
+++ b/chrome/browser/apps/guest_view/web_view_browsertest.cc
@@ -1481,7 +1481,13 @@ IN_PROC_BROWSER_TEST_P(WebViewTest, Shim_TestNestedCrossOriginSubframes) {
              "web_view/shim", NEEDS_TEST_SERVER);
 }
 
-IN_PROC_BROWSER_TEST_P(WebViewTest, Shim_TestNestedSubframes) {
+#if defined(OS_MACOSX)
+// Flaky on Mac. See https://crbug.com/674904.
+#define MAYBE_Shim_TestNestedSubframes DISABLED_Shim_TestNestedSubframes
+#else
+#define MAYBE_Shim_TestNestedSubframes Shim_TestNestedSubframes
+#endif
+IN_PROC_BROWSER_TEST_P(WebViewTest, MAYBE_Shim_TestNestedSubframes) {
   TestHelper("testNestedSubframes", "web_view/shim", NO_TEST_SERVER);
 }