Reland "[Sharesheet] Run file manager browser tests with sharesheet enable."

This reverts commit f878d2a2.

Reason for revert: Re-enabling flag for M89

Original change's description:
> Revert "[Sharesheet] Run file manager browser tests with sharesheet enable."
>
> This reverts commit efbf947b.
>
> Reason for revert: Reverting because we are disabling sharesheet flags by default. 
> Original change's description:
> > [Sharesheet] Run file manager browser tests with sharesheet enable.
> >
> > This CL updates the option.enable_sharesheet default value to be true to
> > run all tests with sharesheet enabled. This is because we turn on the
> > sharesheet flags by default.
> >
> > BUG=1097623
> >
> > Change-Id: I8714da4bffa30992ca0caf40a34b5237423c34b3
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2461666
> > Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
> > Commit-Queue: Maggie Cai <mxcai@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#816074}
>
> TBR=lucmult@chromium.org,mxcai@chromium.org
>
> # Not skipping CQ checks because original CL landed > 1 day ago.
>
> Bug: 1097623
> Change-Id: I48580601e1287ae27b3c8be32e199963b8cdc713
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2501164
> Reviewed-by: Melissa Zhang <melzhang@chromium.org>
> Reviewed-by: Noel Gordon <noel@chromium.org>
> Reviewed-by: Maggie Cai <mxcai@chromium.org>
> Commit-Queue: Noel Gordon <noel@chromium.org>
> Commit-Queue: Melissa Zhang <melzhang@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#821095}

TBR=noel@chromium.org,lucmult@chromium.org,mxcai@chromium.org,melzhang@chromium.org

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

Bug: 1097623
Change-Id: I58c0f13790f66cf337058864eec850078a7ecfa7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2543862Reviewed-by: Melissa Zhang <melzhang@chromium.org>
Commit-Queue: Melissa Zhang <melzhang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828087}

chrome/browser/chromeos/file_manager/file_manager_browsertest_base.h

@@ -107,7 +107,7 @@ class FileManagerBrowserTestBase : public content::DevToolsAgentHostObserver,
     bool observe_file_tasks = true;
 
     // Whether test should enable sharesheet.
-    bool enable_sharesheet = false;
+    bool enable_sharesheet = true;
 
     // Whether test needs the single partition format feature.
     bool single_partition_format = false;