Disable window occlusion APIs when running browser tests

content/public/test/browser_test_base.cc

Index: content/public/test/browser_test_base.cc
diff --git a/content/public/test/browser_test_base.cc b/content/public/test/browser_test_base.cc
index 2e6500a8830a2763cee56e3bf4b2ee8f908c1776..7b7513aabb472ba4d9075127381132ea4323aed3 100644
--- a/content/public/test/browser_test_base.cc
+++ b/content/public/test/browser_test_base.cc
@@ -200,6 +200,11 @@ void BrowserTestBase::SetUp() {
   if (use_software_compositing_)
     command_line->AppendSwitch(switches::kDisableGpu);
 
+  // The layout of windows on screen is unpredictable during tests, so disable
+  // occlusion when running browser tests.
+  base::CommandLine::ForCurrentProcess()->AppendSwitch(
+      switches::kDisableBackgroundingOccludedWindowsForTesting);
+
 #if defined(USE_AURA)
   // Most tests do not need pixel output, so we don't produce any. The command
   // line can override this behaviour to allow for visual debugging.