Re-enable AFDO profiles for Chromecast

After https://chromium-review.googlesource.com/c/chromium/src/+/2486075,
we need to re-enable the default AFDO profile.

Bug: internal b/171409488
Test: CQ
Change-Id: I6a9d1e27e337bb84404edf3a94b6189dd18dd0b0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2519720Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Sean Topping <seantopping@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824161}

build/config/compiler/BUILD.gn

@@ -90,7 +90,7 @@ declare_args() {
   # nonsensical for said projects.
   clang_use_default_sample_profile =
       chrome_pgo_phase == 0 && build_with_chromium && is_official_build &&
-      (is_android || chromeos_is_browser_only)
+      (is_android || chromeos_is_browser_only || is_chromecast)
 
   # This configuration is used to select a default profile in Chrome OS based on
   # the microarchitectures we are using. This is only used if
@@ -2196,9 +2196,10 @@ if (is_clang && is_a_target_toolchain) {
   } else if (clang_use_default_sample_profile) {
     assert(build_with_chromium,
            "Our default profiles currently only apply to Chromium")
-    assert(is_android || chromeos_is_browser_only || is_chromeos,
+    assert(
+        is_android || chromeos_is_browser_only || is_chromeos || is_chromecast,
         "The current platform has no default profile")
-    if (is_android) {
+    if (is_android || is_chromecast) {
       _clang_sample_profile = "//chrome/android/profiles/afdo.prof"
     } else {
       # TODO(crbug/1135245): Remove silvermont, airmont and broadwell after