Mojo C++ bindings: make Array/Map/String non-null by default.

Array<X> a;  // Default construct an empty array.
Array<X> b(nullptr);  // Construct a null array.

a.clear();  // Set to an empty array.
a = nullptr;  // Set to a null array.

BUG=579634
TEST=None

Review URL: https://codereview.chromium.org/1693943002

Cr-Commit-Position: refs/heads/master@{#375304}

7 files changed, 9 insertions, 12 deletions

diff --git a/components/filesystem/directory_impl.cc b/components/filesystem/directory_impl.cc
index 7fd7a4c..3b4e74d 100644
--- a/components/filesystem/directory_impl.cc
+++ b/components/filesystem/directory_impl.cc
@@ -30,7 +30,7 @@ DirectoryImpl::~DirectoryImpl() {
 }
 
 void DirectoryImpl::Read(const ReadCallback& callback) {
-  mojo::Array<DirectoryEntryPtr> entries(0);
+  mojo::Array<DirectoryEntryPtr> entries;
   base::FileEnumerator directory_enumerator(
       directory_path_, false,
       base::FileEnumerator::DIRECTORIES | base::FileEnumerator::FILES);
@@ -221,18 +221,18 @@ void DirectoryImpl::ReadEntireFile(const mojo::String& raw_path,
   base::FilePath path;
   FileError error = ValidatePath(raw_path, directory_path_, &path);
   if (error != FileError::OK) {
-    callback.Run(error, mojo::Array<uint8_t>(0));
+    callback.Run(error, mojo::Array<uint8_t>());
     return;
   }
 
   if (base::DirectoryExists(path)) {
-    callback.Run(FileError::NOT_A_FILE, mojo::Array<uint8_t>(0));
+    callback.Run(FileError::NOT_A_FILE, mojo::Array<uint8_t>());
     return;
   }
 
   base::File base_file(path, base::File::FLAG_OPEN | base::File::FLAG_READ);
   if (!base_file.IsValid()) {
-    callback.Run(GetError(base_file), mojo::Array<uint8_t>(0));
+    callback.Run(GetError(base_file), mojo::Array<uint8_t>());
     return;
   }
 
diff --git a/components/mus/public/cpp/lib/window.cc b/components/mus/public/cpp/lib/window.cc
index 8c2ec50..1f8f3ea 100644
--- a/components/mus/public/cpp/lib/window.cc
+++ b/components/mus/public/cpp/lib/window.cc
@@ -495,7 +495,7 @@ void Window::SetSharedPropertyInternal(const std::string& name,
     return;
 
   if (connection_) {
-    mojo::Array<uint8_t> transport_value;
+    mojo::Array<uint8_t> transport_value(nullptr);
     if (value) {
       transport_value.resize(value->size());
       if (value->size())
diff --git a/components/mus/public/cpp/lib/window_tree_client_impl.cc b/components/mus/public/cpp/lib/window_tree_client_impl.cc
index 0a7426f..2d609fe 100644
--- a/components/mus/public/cpp/lib/window_tree_client_impl.cc
+++ b/components/mus/public/cpp/lib/window_tree_client_impl.cc
@@ -299,7 +299,7 @@ void WindowTreeClientImpl::SetProperty(Window* window,
                                        mojo::Array<uint8_t> data) {
   DCHECK(tree_);
 
-  mojo::Array<uint8_t> old_value;
+  mojo::Array<uint8_t> old_value(nullptr);
   if (window->HasSharedProperty(name))
     old_value = mojo::Array<uint8_t>::From(window->properties_[name]);
 
@@ -435,8 +435,6 @@ Window* WindowTreeClientImpl::NewWindowImpl(
   if (properties) {
     transport_properties =
         mojo::Map<mojo::String, mojo::Array<uint8_t>>::From(*properties);
-  } else {
-    transport_properties.mark_non_null();
   }
   if (type == NewWindowType::CHILD) {
     tree_->NewWindow(change_id, window->id(), std::move(transport_properties));
diff --git a/components/mus/public/cpp/tests/window_tree_client_impl_unittest.cc b/components/mus/public/cpp/tests/window_tree_client_impl_unittest.cc
index c1159d5..dc19a84 100644
--- a/components/mus/public/cpp/tests/window_tree_client_impl_unittest.cc
+++ b/components/mus/public/cpp/tests/window_tree_client_impl_unittest.cc
@@ -62,7 +62,7 @@ class WindowTreeClientImplPrivate {
     root_data->parent_id = 0;
     root_data->window_id = 1;
     root_data->bounds = mojo::Rect::From(gfx::Rect());
-    root_data->properties.mark_non_null();
+    root_data->properties.SetToEmpty();
     root_data->visible = true;
     root_data->drawn = true;
     root_data->viewport_metrics = mojom::ViewportMetrics::New();
diff --git a/components/mus/ws/window_tree_apptest.cc b/components/mus/ws/window_tree_apptest.cc
index bc55a76..ee2a186 100644
--- a/components/mus/ws/window_tree_apptest.cc
+++ b/components/mus/ws/window_tree_apptest.cc
@@ -234,7 +234,7 @@ class TestWindowTreeClientImpl : public mojom::WindowTreeClient,
   bool SetWindowProperty(Id window_id,
                          const std::string& name,
                          const std::vector<uint8_t>* data) {
-    Array<uint8_t> mojo_data;
+    Array<uint8_t> mojo_data(nullptr);
     if (data)
       mojo_data = Array<uint8_t>::From(*data);
     const uint32_t change_id = GetAndAdvanceChangeId();
diff --git a/components/mus/ws/window_tree_impl.cc b/components/mus/ws/window_tree_impl.cc
index df73c46..f144d3a 100644
--- a/components/mus/ws/window_tree_impl.cc
+++ b/components/mus/ws/window_tree_impl.cc
@@ -397,7 +397,7 @@ void WindowTreeImpl::ProcessWindowPropertyChanged(
   if (!IsWindowKnown(window, &client_window_id))
     return;
 
-  Array<uint8_t> data;
+  Array<uint8_t> data(nullptr);
   if (new_data)
     data = Array<uint8_t>::From(*new_data);
 
diff --git a/components/mus/ws/window_tree_unittest.cc b/components/mus/ws/window_tree_unittest.cc
index 8eea452..99e53a5 100644
--- a/components/mus/ws/window_tree_unittest.cc
+++ b/components/mus/ws/window_tree_unittest.cc
@@ -849,7 +849,6 @@ TEST_F(WindowTreeTest, NewTopLevelWindow) {
 
   // Create a new top level window.
   mojo::Map<mojo::String, mojo::Array<uint8_t>> properties;
-  properties.mark_non_null();
   const uint32_t initial_change_id = 17;
   // Explicitly use an id that does not contain the connection id.
   const ClientWindowId embed_window_id2_in_child(45 << 16 | 27);