Revert "Remove unnecessary call to EnableFileSystemInGuestMode"

This reverts commit e0ffa06d.

Reason for revert: <INSERT REASONING HERE>
Bug: 891889

Original change's description:
> Remove unnecessary call to EnableFileSystemInGuestMode
> 
> This call makes no sense. There's no reason that loading the
> speech synthesis component extension should trigger enabling
> the filesystem in guest mode for a related, but entirely different,
> extension (ChromeVox).
> 
> If ChromeVox needs EnableFileSystemInGuestMode, we should be calling
> this from code that loads the ChromeVox component extension, but I suspect
> that it doesn't need it at all.
> 
> As far as I can tell this was accidentally added here as part of a
> refactoring:
>   https://codereview.chromium.org/1162283002
> 
> Note that OnceClosure() would be better, but that'd require a big cleanup
> of many other functions, so I don't want to do that as part of the same
> change.
> 
> Bug: none
> Change-Id: I1f67b78548048fffa9194083b10e0ff5c5aaa863
> Reviewed-on: https://chromium-review.googlesource.com/1246364
> Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
> Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#594463}

TBR=dmazzoni@chromium.org,dtseng@chromium.org,rdevlin.cronin@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: none
Change-Id: If18c5fcbdbc6be5b6ce8235afa612597792127ff
Reviewed-on: https://chromium-review.googlesource.com/c/1261960Reviewed-by: David Tseng <dtseng@chromium.org>
Commit-Queue: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596731}

chrome/browser/extensions/component_loader.cc

@@ -365,7 +365,10 @@ void ComponentLoader::AddNetworkSpeechSynthesisExtension() {
 void ComponentLoader::AddChromeOsSpeechSynthesisExtension() {
   AddComponentFromDir(
       base::FilePath(extension_misc::kSpeechSynthesisExtensionPath),
-      extension_misc::kSpeechSynthesisExtensionId, base::RepeatingClosure());
+      extension_misc::kSpeechSynthesisExtensionId,
+      base::Bind(&ComponentLoader::EnableFileSystemInGuestMode,
+                 weak_factory_.GetWeakPtr(),
+                 extension_misc::kChromeVoxExtensionId));
 }
 #endif