Attempt 2: Allows tab dragging when maximized on aura. To fix it I made it so

ash/wm/workspace/workspace_layout_manager.cc

Index: ash/wm/workspace/workspace_layout_manager.cc
diff --git a/ash/wm/workspace/workspace_layout_manager.cc b/ash/wm/workspace/workspace_layout_manager.cc
index 0ac362cda8f2b5183630dee9406a5538fcb0d973..b1f8f6605cf12258670411d0b39e58b76098b21c 100644
--- a/ash/wm/workspace/workspace_layout_manager.cc
+++ b/ash/wm/workspace/workspace_layout_manager.cc
@@ -8,6 +8,7 @@
 #include "ash/wm/window_util.h"
 #include "ash/wm/workspace/workspace.h"
 #include "ash/wm/workspace/workspace_manager.h"
+#include "ash/wm/workspace/workspace_window_resizer.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/event.h"
 #include "ui/aura/root_window.h"
@@ -29,13 +30,19 @@ WorkspaceLayoutManager::WorkspaceLayoutManager(
     : workspace_manager_(workspace_manager) {
 }
 
-WorkspaceLayoutManager::~WorkspaceLayoutManager() {}
+WorkspaceLayoutManager::~WorkspaceLayoutManager() {
+  const aura::Window::Windows& windows(
+      workspace_manager_->contents_view()->children());
+  for (size_t i = 0; i < windows.size(); ++i)
+    windows[i]->RemoveObserver(this);
+}
 
 void WorkspaceLayoutManager::OnWindowResized() {
   // Workspace is updated via RootWindowObserver::OnRootWindowResized.
 }
 
 void WorkspaceLayoutManager::OnWindowAddedToLayout(aura::Window* child) {
+  child->AddObserver(this);
   if (!workspace_manager_->IsManagedWindow(child))
     return;
 
@@ -56,6 +63,7 @@ void WorkspaceLayoutManager::OnWindowAddedToLayout(aura::Window* child) {
 
 void WorkspaceLayoutManager::OnWillRemoveWindowFromLayout(
     aura::Window* child) {
+  child->RemoveObserver(this);
   ClearRestoreBounds(child);
   workspace_manager_->RemoveWindow(child);
 }
@@ -75,16 +83,29 @@ void WorkspaceLayoutManager::SetChildBounds(
     aura::Window* child,
     const gfx::Rect& requested_bounds) {
   gfx::Rect child_bounds(requested_bounds);
-  if (wm::IsWindowMaximized(child)) {
-    child_bounds = gfx::Screen::GetMonitorWorkAreaNearestWindow(child);
-  } else if (wm::IsWindowFullscreen(child)) {
-    child_bounds = gfx::Screen::GetMonitorAreaNearestWindow(child);
-  } else {
-    child_bounds = gfx::Screen::GetMonitorWorkAreaNearestWindow(child).
-        AdjustToFit(requested_bounds);
+  if (GetTrackedByWorkspace(child)) {
+    if (wm::IsWindowMaximized(child)) {
+      child_bounds = gfx::Screen::GetMonitorWorkAreaNearestWindow(child);
+    } else if (wm::IsWindowFullscreen(child)) {
+      child_bounds = gfx::Screen::GetMonitorAreaNearestWindow(child);
+    } else {
+      child_bounds = gfx::Screen::GetMonitorWorkAreaNearestWindow(child).
+          AdjustToFit(requested_bounds);
+    }
   }
   SetChildBoundsDirect(child, child_bounds);
 }
 
+void WorkspaceLayoutManager::OnWindowPropertyChanged(aura::Window* window,
+                                                     const void* key,
+                                                     intptr_t old) {
+  if (key == ash::kWindowTrackedByWorkspaceSplitPropKey &&
+      ash::GetTrackedByWorkspace(window)) {
+    // We currently don't need to support transitioning from true to false, so
+    // we ignore it.
+    workspace_manager_->AddWindow(window);
+  }
+}
+
 }  // namespace internal
 }  // namespace ash