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

ash/wm/workspace/workspace_layout_manager.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/wm/workspace/workspace_layout_manager.h"
 
 #include "ash/wm/property_util.h"
 #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"
 #include "ui/aura/screen_aura.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_observer.h"
 #include "ui/base/ui_base_types.h"
 #include "ui/gfx/rect.h"
 #include "ui/views/widget/native_widget_aura.h"
 
 namespace ash {
 namespace internal {
 
 ////////////////////////////////////////////////////////////////////////////////
 // WorkspaceLayoutManager, public:
 
 WorkspaceLayoutManager::WorkspaceLayoutManager(
     WorkspaceManager* workspace_manager)
     : 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;
 
   if (child->IsVisible()) {
     workspace_manager_->AddWindow(child);
   } else if (wm::IsWindowMaximized(child)) {
     SetChildBoundsDirect(child,
                          gfx::Screen::GetMonitorWorkAreaNearestWindow(child));
   } else if (wm::IsWindowFullscreen(child)) {
     SetChildBoundsDirect(child,
                          gfx::Screen::GetMonitorAreaNearestWindow(child));
   } else {
     // Align non-maximized/fullscreen windows to a grid.
     SetChildBoundsDirect(
         child, workspace_manager_->AlignBoundsToGrid(child->GetTargetBounds()));
   }
 }
 
 void WorkspaceLayoutManager::OnWillRemoveWindowFromLayout(
     aura::Window* child) {
+  child->RemoveObserver(this);
   ClearRestoreBounds(child);
   workspace_manager_->RemoveWindow(child);
 }
 
 void WorkspaceLayoutManager::OnChildWindowVisibilityChanged(
     aura::Window* child,
     bool visible) {
   if (!workspace_manager_->IsManagedWindow(child))
     return;
   if (visible)
     workspace_manager_->AddWindow(child);
   else
     workspace_manager_->RemoveWindow(child);
 }
 
 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