Web Share For Chrome OS: ShareTwoFiles tests ../ in path

SharesheetClientBrowserTest::ShareTwoFiles uses script to
share a file named '../sample.mp4'.

We verify that this becomes a filename beginning with 'share',
with no directory escape.

Change-Id: I731afa6e7e0c071b83eac8b461d382acad6cac93
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2567869
Commit-Queue: Eric Willigers <ericwilligers@chromium.org>
Reviewed-by: Alan Cutter <alancutter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834087}

chrome/browser/webshare/chromeos/store_file_task.cc

@@ -4,6 +4,7 @@
 
 #include "chrome/browser/webshare/chromeos/store_file_task.h"
 
+#include "base/strings/string_util.h"
 #include "base/threading/scoped_blocking_call.h"
 
 namespace webshare {
@@ -17,7 +18,11 @@ StoreFileTask::StoreFileTask(base::FilePath filename,
       available_space_(available_space),
       callback_(std::move(callback)),
       read_pipe_watcher_(FROM_HERE,
-                         mojo::SimpleWatcher::ArmingPolicy::AUTOMATIC) {}
+                         mojo::SimpleWatcher::ArmingPolicy::AUTOMATIC) {
+  // |filename| is generated by GenerateFileName().
+  DCHECK(!filename_.ReferencesParent());
+  DCHECK(base::StartsWith(filename_.BaseName().MaybeAsASCII(), "share"));
+}
 
 StoreFileTask::~StoreFileTask() = default;
 

chrome/test/data/webshare/index.html

@@ -33,7 +33,7 @@
     async function share_multiple_files() {
       try {
         const first_file = create_file('sample.mp3', 'audio/mp3', 345);
-        const second_file = create_file('sample.mp4', 'video/mp4', 67890);
+        const second_file = create_file('../sample.mp4', 'video/mp4', 67890);
         await navigator.share({files: [first_file, second_file]});
         return 'share succeeded';
       } catch(error) {