Include absl's optional.h in first-party headers.

Many first-party headers reference absl::optional but does not include
the header. Fix this mechanically using the file list generated as
follows:

git ls-files | grep '\.h$' | grep -v third_party | \
    xargs grep -l absl::optional | \
    xargs grep -L '//.*absl::optional' | \
    xargs grep -L override | \
    xargs grep -L '^#include "third_party/abseil-cpp/absl/types/optional\.h"'

Change-Id: I7693f707a416d3088f7cde22cd07b1458c4c5405
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2911952
Reviewed-by: Peter Kasting <[email protected]>
Commit-Queue: Peter Kasting <[email protected]>
Owners-Override: Peter Kasting <[email protected]>
Cr-Commit-Position: refs/heads/master@{#885381}
diff --git a/chromeos/components/drivefs/drivefs_search.h b/chromeos/components/drivefs/drivefs_search.h
index 6e487d6..533298e 100644
--- a/chromeos/components/drivefs/drivefs_search.h
+++ b/chromeos/components/drivefs/drivefs_search.h
@@ -15,6 +15,7 @@
 #include "base/time/clock.h"
 #include "chromeos/components/drivefs/mojom/drivefs.mojom.h"
 #include "mojo/public/cpp/bindings/remote.h"
+#include "third_party/abseil-cpp/absl/types/optional.h"
 
 namespace network {
 class NetworkConnectionTracker;