arc: Handle invalid dummy FD in ProtectedBufferManager

This CL makes ProtectedBufferManager::ImportDummyFd() handle an invalid
|dummy_fd| and ensures that all the call sites of that method handle a
nullptr return value.

Bug: b:195769334
Test: None
Change-Id: Ie487e8c6018c61d87c3cdd742713d25a5769674d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3397512
Reviewed-by: Chih-Yu Huang <akahuang@chromium.org>
Commit-Queue: Andres Calderon Jaramillo <andrescj@chromium.org>
Cr-Commit-Position: refs/heads/main@{#961207}

ash/components/arc/video_accelerator/protected_buffer_manager.cc

@@ -404,6 +404,8 @@ ProtectedBufferManager::GetProtectedSharedMemoryRegionFor(
     base::ScopedFD dummy_fd) {
   uint32_t id = 0;
   auto pixmap = ImportDummyFd(std::move(dummy_fd), &id);
+  if (!pixmap)
+    return {};
 
   base::AutoLock lock(buffer_map_lock_);
   const auto& iter = buffer_map_.find(id);
@@ -418,6 +420,8 @@ ProtectedBufferManager::GetProtectedNativePixmapHandleFor(
     base::ScopedFD dummy_fd) {
   uint32_t id = 0;
   auto pixmap = ImportDummyFd(std::move(dummy_fd), &id);
+  if (!pixmap)
+    return gfx::NativePixmapHandle();
 
   base::AutoLock lock(buffer_map_lock_);
   const auto& iter = buffer_map_.find(id);
@@ -451,6 +455,8 @@ ProtectedBufferManager::GetProtectedNativePixmapFor(
   base::ScopedFD dummy_fd(HANDLE_EINTR(dup(handle.planes[0].fd.get())));
   uint32_t id = 0;
   auto pixmap = ImportDummyFd(std::move(dummy_fd), &id);
+  if (!pixmap)
+    return nullptr;
 
   base::AutoLock lock(buffer_map_lock_);
   const auto& iter = buffer_map_.find(id);
@@ -477,6 +483,8 @@ scoped_refptr<gfx::NativePixmap> ProtectedBufferManager::ImportDummyFd(
     uint32_t* id) const {
   // 0 is an invalid handle id.
   *id = 0;
+  if (!dummy_fd.is_valid())
+    return nullptr;
 
   // Import dummy_fd to acquire its unique id.
   // CreateNativePixmapFromHandle() takes ownership and will close the handle