Moving a tab uses CMD key on Mac.

When in keyboard accessibility mode, with a tab keyboard-focused,
pressing CTRL-LEFT or CTRL-RIGHT moves a tab left or right; holding
SHIFT as well moves the tab first or last.

On Mac, since CTRL keys are used to do things like swapping workspaces
we now instead use combinations with the CMD key.

Bug: 996850
Change-Id: I08443c066f6998eb4bfff3fea7ab5be56b005d43
Fixes: 996850
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1949205
Auto-Submit: Dana Fried <dfried@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Dana Fried <dfried@chromium.org>
Cr-Commit-Position: refs/heads/master@{#721162}

chrome/browser/ui/views/tabs/tab.cc

@@ -428,8 +428,14 @@ bool Tab::OnKeyPressed(const ui::KeyEvent& event) {
     return true;
   }
 
-  if (event.type() == ui::ET_KEY_PRESSED &&
-      (event.flags() & ui::EF_CONTROL_DOWN)) {
+  constexpr int kModifiedFlag =
+#if defined(OS_MACOSX)
+      ui::EF_COMMAND_DOWN;
+#else
+      ui::EF_CONTROL_DOWN;
+#endif
+
+  if (event.type() == ui::ET_KEY_PRESSED && (event.flags() & kModifiedFlag)) {
     if (event.flags() & ui::EF_SHIFT_DOWN) {
       if (event.key_code() == ui::VKEY_RIGHT) {
         controller()->MoveTabLast(this);