Windows docking should get triggered by pressing against the screen edge

ash/wm/workspace/snap_sizer.h

Index: ash/wm/workspace/snap_sizer.h
diff --git a/ash/wm/workspace/snap_sizer.h b/ash/wm/workspace/snap_sizer.h
index bd5f719ae482d1d78be1c20d70fd0895e3eb0703..b4cae25739b8dc244593816fa3af0a1a5e2629e5 100644
--- a/ash/wm/workspace/snap_sizer.h
+++ b/ash/wm/workspace/snap_sizer.h
@@ -19,6 +19,8 @@ class Window;
 namespace ash {
 namespace internal {
 
+class DockedWindowLayoutManager;
+
 // SnapSizer is responsible for determining the resulting bounds of a window
 // that is being snapped to the left or right side of the screen.
 // The bounds used in this class are in the container's coordinates.
@@ -31,6 +33,7 @@ class ASH_EXPORT SnapSizer {
 
   enum InputType {
     TOUCH_MAXIMIZE_BUTTON_INPUT,
+    WORKSPACE_DRAG_INPUT,
     OTHER_INPUT
   };
 
@@ -63,6 +66,13 @@ class ASH_EXPORT SnapSizer {
   // For unit test purposes this function is not private.
   gfx::Rect GetTargetBoundsForSize(size_t size_index) const;
 
+  // Returns true when snapping sequence is at its last (docking) step.

[sky, 2013/09/11 19:38:40]

Why do we need snapsizer to know about docked windows? Could we keep this class
at only the snap behavior and transition to another one when we need to dock?

[varkha, 2013/09/11 20:02:10]

We moved to the model where docking is the last step in tiling sequence. Most of
the logic that deals with iterating along the sequence still applies. I agree
that most of the awareness about docked layout can be weeded out (it is in
CanWindowDock which is static and can be taken out easily) but I think the
docking guide target bounds can stay in this class for both tiled and docked
cases. This simplifies the resizer logic and leaves concerns better separated in
the resizer chain.
Consider that with a mouse drag it is possible to go back and forth between
tiling and docking and this simple class is all that coordinates those.

[varkha, 2013/09/12 19:49:23]

Done.

+  bool ShouldDockWindow() const;
+
+  // Returns true when a window can be docked. Windows cannot be docked at the
+  // edge used by the launcher shelf or the edge opposite from existing dock.
+  static bool CanDockWindow(aura::Window* window, SnapSizer::Edge edge);
+
  private:
   // Calculates the amount to increment by. This returns one of -1, 0 or 1 and
   // is intended to by applied to |size_index_|. |x| is the current
@@ -81,6 +91,10 @@ class ASH_EXPORT SnapSizer {
   // Returns true if the specified point is along the edge of the screen.
   bool AlongEdge(int x) const;
 
+  // Dock when a window is at its last step in snapping sequence, undock
+  // otherwise.
+  void UpdateDockedState();
+
   // Window being snapped.
   aura::Window* window_;
 
@@ -118,8 +132,12 @@ class ASH_EXPORT SnapSizer {
   const InputType input_type_;
 
   // A list of usable window widths for size. This gets created when the
-  // sizer gets created.
-  const std::vector<int> usable_width_;
+  // sizer gets created. Possible last 0 entry indicates that computing bounds
+  // needs to be delegated to DockedWindowLayoutManager.
+  std::vector<int> usable_width_;
+
+  // Dock container window layout manager.
+  DockedWindowLayoutManager* dock_layout_;
 
   DISALLOW_COPY_AND_ASSIGN(SnapSizer);
 };