Disable ProcessManagerBrowserTest.KeepaliveOnNetworkRequest on Linux

Disabled for flaky failures.

TBR=rockot@google.com

Bug: 1030435
Change-Id: I1a1935eaf0bb35c2109c6ff74fc1f1c5ab133581
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1948917
Commit-Queue: Takumi Fujimoto <takumif@chromium.org>
Reviewed-by: Takumi Fujimoto <takumif@chromium.org>
Cr-Commit-Position: refs/heads/master@{#721219}

chrome/browser/extensions/process_manager_browsertest.cc

@@ -671,7 +671,14 @@ IN_PROC_BROWSER_TEST_F(ProcessManagerBrowserTest,
 
 // Verify correct keepalive count behavior on network request events.
 // Regression test for http://crbug.com/535716.
-IN_PROC_BROWSER_TEST_F(ProcessManagerBrowserTest, KeepaliveOnNetworkRequest) {
+// Disabled on Linux for flakiness: http://crbug.com/1030435.
+#if defined(OS_LINUX)
+#define MAYBE_KeepaliveOnNetworkRequest DISABLED_KeepaliveOnNetworkRequest
+#else
+#define MAYBE_KeepaliveOnNetworkRequest KeepaliveOnNetworkRequest
+#endif
+IN_PROC_BROWSER_TEST_F(ProcessManagerBrowserTest,
+                       MAYBE_KeepaliveOnNetworkRequest) {
   // Load an extension with a lazy background page.
   scoped_refptr<const Extension> extension =
       LoadExtension(test_data_dir_.AppendASCII("api_test")