Enable /GL for all targets in Official (behind a flag)

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 3ee4412ed255fbde3e0b94f81b767bd353851eac..9d2aedab1e459a47e04f7324abf8d5a6f55186dc 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -71,6 +71,9 @@ declare_args() {
     # it has, then we don't need to disable 4702 (unreachable code warning).
     # The patch is preapplied to the internal toolchain and hence all bots.
     msvs_xtree_patched = false
+
+    # Whether or not the official builds should be build with full WPO.
+    full_wpo_on_official = false
   }
 
   # Omit unwind support in official builds to save space.
@@ -1233,12 +1236,9 @@ if (is_win) {
 # Default "optimization on" config.
 config("optimize") {
   if (is_win) {
-    # TODO(sebmarchand): Enable this once we've decided to ship with full WPO
-    # and when the change to the incompatible projects (FFmpeg and Yasm) have
-    # have been committed.
-    #if (is_official_build) {
-    #  common_optimize_on_cflags += [ "/GL" ]
-    #}
+    if (is_official_build && full_wpo_on_official) {
+      common_optimize_on_cflags += [ "/GL" ]
+    }
 
     # Favor size over speed, /O1 must be before the common flags. The GYP
     # build also specifies /Os and /GF but these are implied by /O1.