Do not lose secondary gpus and make sure to have an active gpu on multiple gpu configurations

gpu/config/gpu_switches.cc

Index: gpu/config/gpu_switches.cc
diff --git a/gpu/config/gpu_switches.cc b/gpu/config/gpu_switches.cc
index 554582d81aaf4bd2b14a520a4bb86c7f875a19a9..819f516d259ba923ed1545e12bd9659217d72501 100644
--- a/gpu/config/gpu_switches.cc
+++ b/gpu/config/gpu_switches.cc
@@ -22,6 +22,12 @@ const char kGpuTestingVendorId[] = "gpu-testing-vendor-id";
 // Override gpu device id from the GpuInfoCollector.
 const char kGpuTestingDeviceId[] = "gpu-testing-device-id";
 
+// Override secondary gpu vendor id from the GpuInfoCollector.
+const char kGpuTestingSecondaryVendorId[] = "gpu-testing-secondary-vendor-id";
+
+// Override secondary gpu device id from the GpuInfoCollector.
+const char kGpuTestingSecondaryDeviceId[] = "gpu-testing-secondary-device-id";
+
 // Override gl vendor from the GpuInfoCollector.
 const char kGpuTestingGLVendor[] = "gpu-testing-gl-vendor";