Trigger AvatarToolbarButton menu on LMB press

This makes the AvatarToolbarButton toggle like a MenuButton similarly to
the adjacent BrowserAppMenuButton (which is actually a MenuButton).

Bug: chromium:849911
Change-Id: I30690c61dd9b9b58b80e28dcbc85dc9e72835b9d
Reviewed-on: https://chromium-review.googlesource.com/1091592
Commit-Queue: Peter Boström <pbos@chromium.org>
Reviewed-by: Bret Sepulveda <bsep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565440}

chrome/browser/ui/views/profiles/avatar_toolbar_button.cc

@@ -47,8 +47,11 @@ AvatarToolbarButton::AvatarToolbarButton(Profile* profile,
   if (!ui::MaterialDesignController::IsTouchOptimizedUiEnabled())
     SetBorder(views::CreateEmptyBorder(gfx::Insets(4)));
 
-  set_triggerable_event_flags(ui::EF_LEFT_MOUSE_BUTTON |
-                              ui::EF_MIDDLE_MOUSE_BUTTON);
+  // Activate on press for left-mouse-button only to mimic other MenuButtons
+  // without drag-drop actions (specifically the adjacent browser menu).
+  set_notify_action(Button::NOTIFY_ON_PRESS);
+  set_triggerable_event_flags(ui::EF_LEFT_MOUSE_BUTTON);
+
   set_tag(IDC_SHOW_AVATAR_MENU);
   set_id(VIEW_ID_AVATAR_BUTTON);