Reland "Switch the Linux official build to PGO (from AFDO)."

This is a reland of 4be5a8c2

Fix: Disabled PGO for the LaCrOS builds as we don't know if it's what we
want (vs AFDO). If we decide to use PGO for LaCrOS then we'll do it in a
separate CL.

Original change's description:
> Switch the Linux official build to PGO (from AFDO).
>
> This switches the Linux official build from AFDO to PGO. This yield some
> 3-4% performance gains on Speedometer and help unifying our desktop
> build configurations, PGO is already used on Win and Mac. The PGO
> profiles for Linux are generated by a continuous bot and are rolled in
> Chrome once or twice per day (AFDO is based on the Android profiles).
>
> This increases binary size by ~3-4%.
>
> Bug: 1111437
> Change-Id: I565eb336fa5ad9480e99808ed49246634255b82d
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2404620
> Commit-Queue: Sébastien Marchand <sebmarchand@chromium.org>
> Reviewed-by: Nico Weber <thakis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#809040}

Bug: 1111437
Change-Id: I3eb551007d66edb4c9ff326c801dda7e0ddd593c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2424669Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809803}

build/config/compiler/BUILD.gn

@@ -89,7 +89,7 @@ declare_args() {
   # nonsensical for said projects.
   clang_use_default_sample_profile =
       chrome_pgo_phase == 0 && build_with_chromium && is_official_build &&
-      (is_android || is_desktop_linux)
+      (is_android || chromeos_is_browser_only)
 
   # This configuration is used to select a default profile in Chrome OS based on
   # the microarchitectures we are using. This is only used if

build/config/compiler/pgo/pgo.gni

@@ -2,6 +2,8 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/config/chromeos/ui_mode.gni")
+
 declare_args() {
   # Specify the current PGO phase.
   # Here's the different values that can be used:
@@ -9,7 +11,8 @@ declare_args() {
   #     1 : Used during the PGI (instrumentation) phase.
   #     2 : Used during the PGO (optimization) phase.
   chrome_pgo_phase = 0
-  if (is_official_build && (is_win || is_mac)) {
+  if (is_official_build &&
+      (is_win || is_mac || (is_desktop_linux && !chromeos_is_browser_only))) {
     chrome_pgo_phase = 2
   }