Add a PGO tag for the PGO builds in chrome://version

chrome/common/features.gni

Index: chrome/common/features.gni
diff --git a/chrome/common/features.gni b/chrome/common/features.gni
index 890cde193c2fa84f3475bf6b9fcc253f7cb9b4d2..d36b6ae72241f9f78315f2f617948051d0ca47d2 100644
--- a/chrome/common/features.gni
+++ b/chrome/common/features.gni
@@ -6,6 +6,7 @@
 # Please keep in sync!
 
 import("//build/config/chromecast_build.gni")
+import("//build/config/compiler/compiler.gni")
 
 declare_args() {
   enable_google_now = !is_ios && !is_android && !is_chromecast
@@ -29,6 +30,9 @@ declare_args() {
   # Set to true to bundle all the mash related mojo services into chrome.
   # Specify --mash to chrome to have chrome start the mash environment.
   enable_package_mash_services = is_chromeos
+
+  # Indicates if the build is using PGO.
+  pgo_build = chrome_pgo_phase > 0
 }
 
 chrome_grit_defines = [