xkblayoutengine: fix memory leak by unrefing keymap from buffer.

Wayland may supply xkb layout engine with a keymap that it creates
from a buffer. However, when I ran events_unittests with asan,
it noticed a memory leak, which was caused by not freed keymap
object.

As long as we can have only one keymap from buffer at a time,
store each keymap after a new context is created as unique_ptr
that will be freed with a custom deleter on either dtor or when
another keymap is created.

Bug: 1120270
Change-Id: I741a6cb74713424f54dd858f84c0fec413cd6c44
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2367938Reviewed-by: Michael Spang <spang@chromium.org>
Commit-Queue: Maksim Sisov (GMT+3) <msisov@igalia.com>
Cr-Commit-Position: refs/heads/master@{#800708}

ui/events/ozone/layout/xkb/xkb_keyboard_layout_engine.cc

@@ -816,6 +816,10 @@ bool XkbKeyboardLayoutEngine::SetCurrentLayoutFromBuffer(
     return false;
 
   SetKeymap(keymap);
+
+  // Store the keymap that will be unrefed either on dtor or if a new keymap is
+  // created.
+  key_map_from_buffer_.reset(keymap);
   return true;
 }
 

ui/events/ozone/layout/xkb/xkb_keyboard_layout_engine.h

@@ -22,6 +22,8 @@
 #include "ui/events/ozone/layout/keyboard_layout_engine.h"
 #include "ui/events/ozone/layout/xkb/xkb_key_code_converter.h"
 
+struct xkb_keymap;
+
 namespace ui {
 
 class COMPONENT_EXPORT(EVENTS_OZONE_LAYOUT) XkbKeyboardLayoutEngine
@@ -124,6 +126,9 @@ class COMPONENT_EXPORT(EVENTS_OZONE_LAYOUT) XkbKeyboardLayoutEngine
 
   std::unique_ptr<xkb_context, XkbContextDeleter> xkb_context_;
 
+  // Holds the keymap from xkb_keymap_new_from_buffer.
+  std::unique_ptr<xkb_keymap, XkbKeymapDeleter> key_map_from_buffer_;
+
   std::string current_layout_name_;
 
   xkb_layout_index_t layout_index_ = 0;