Add semantics to apply gpu blakclist to AMD swichable when a discrete/integrated GPU is in use

gpu/config/gpu_control_list_format.txt

Index: gpu/config/gpu_control_list_format.txt
diff --git a/gpu/config/gpu_control_list_format.txt b/gpu/config/gpu_control_list_format.txt
index 879b91e2f38ea0208b4ac629c56d2bc22358b91a..71c569c8397eb30fcd6cd31b0f3ffb67e0b4e85a 100644
--- a/gpu/config/gpu_control_list_format.txt
+++ b/gpu/config/gpu_control_list_format.txt
@@ -23,8 +23,12 @@
 //    "version" is a VERSION structure (defined below).
 // 3. "vendor_id" is a string.  0 is reserved.
 // 4. "device_id" is an array of strings.  0 is reserved.
-// 5. "multi_gpu_style" is a string, valid values include "optimus", and
-//    "amd_switchable".
+// 5. "multi_gpu_style" is a string, valid values include:
+//      a) "optimus": NVIDIA dual GPU
+//      b) "amd_switchable": AMD dual GPU
+//      c) "amd_switchable_integrated": AMD dual GPU, integrated GPU is active
+//      d) "amd_switchable_discrete": AMD dual GPU, discrete GPU is active
+//    c) and d) are only valid on Win, as on Mac we can switch GPU on the fly.
 // 6. "multi_gpu_category" is a string, valid values include "any", "primary",
 //    "secondary", and "active". If unspecified, the default value is "primary".
 //    See gpu_control_list.h for more details on the meanings of the strings.