Re-enable CrossSiteIframe test.

BUG=399775

Review URL: https://codereview.chromium.org/555463002

Cr-Commit-Position: refs/heads/master@{#294399}

content/browser/site_per_process_browsertest.cc

@@ -189,10 +189,14 @@ void SitePerProcessBrowserTest::SetUpCommandLine(CommandLine* command_line) {
   command_line->AppendSwitch(switches::kSitePerProcess);
 };
 
-// Ensure that we can complete a cross-process subframe navigation.
-// Crashes ChromeOS bot, but the bug is probably present on other platforms
-// also. http://crbug.com/399775
-IN_PROC_BROWSER_TEST_F(SitePerProcessBrowserTest, DISABLED_CrossSiteIframe) {
+// It fails on ChromeOS and Android, so disabled while investigating.
+// http://crbug.com/399775
+#if defined(OS_ANDROID) || defined(OS_CHROMEOS)
+#define MAYBE_CrossSiteIframe DISABLED_CrossSiteIframe
+#else
+#define MAYBE_CrossSiteIframe CrossSiteIframe
+#endif
+IN_PROC_BROWSER_TEST_F(SitePerProcessBrowserTest, MAYBE_CrossSiteIframe) {
   host_resolver()->AddRule("*", "127.0.0.1");
   ASSERT_TRUE(test_server()->Start());
   GURL main_url(test_server()->GetURL("files/site_per_process_main.html"));