Implemented swipe to close in overview mode.

ash/wm/overview/scoped_transform_overview_window.cc

Index: ash/wm/overview/scoped_transform_overview_window.cc
diff --git a/ash/wm/overview/scoped_transform_overview_window.cc b/ash/wm/overview/scoped_transform_overview_window.cc
index 41205bf64ff8fa666af1e75383bee1332d400f6a..2c2ab62114ab212406c114542d303796b3aacda2 100644
--- a/ash/wm/overview/scoped_transform_overview_window.cc
+++ b/ash/wm/overview/scoped_transform_overview_window.cc
@@ -8,9 +8,11 @@
 #include <vector>
 
 #include "ash/screen_util.h"
+#include "ash/shell.h"
 #include "ash/shell_window_ids.h"
 #include "ash/wm/overview/scoped_overview_animation_settings.h"
 #include "ash/wm/overview/scoped_window_copy.h"
+#include "ash/wm/overview/window_selector_controller.h"
 #include "ash/wm/overview/window_selector_item.h"
 #include "ash/wm/window_state.h"
 #include "ash/wm/window_util.h"
@@ -32,12 +34,25 @@ namespace {
 // The opacity level that windows will be set to when they are restored.
 const float kRestoreWindowOpacity = 1.0f;
 
+// The minimum opacity used during touch scroll gestures.
+const float kMinimumOpacity = 0.2f;
+
+// The distance at which the minimum opacity should take effect.
+const float kMinimumOpacityDistance = 200.0f;
+
 aura::Window* GetTransientRoot(aura::Window* window) {
   while (::wm::GetTransientParent(window))
     window = ::wm::GetTransientParent(window);
   return window;
 }
 
+// Calculates the window opacity from the given scroll |distance|.
+float CalculateOpacityFromScrollDistance(int distance) {
+  float opacity =
+      1.0 - static_cast<float>(abs(distance)) / kMinimumOpacityDistance;
+  return std::min(1.0f, std::max(kMinimumOpacity, opacity));
+}
+
 // An iterator class that traverses an aura::Window and all of it's transient
 // descendants.
 class TransientDescendantIterator {
@@ -165,7 +180,7 @@ TransientDescendantIteratorRange GetTransientTreeIterator(
 }  // namespace
 
 ScopedTransformOverviewWindow::ScopedTransformOverviewWindow(
-        aura::Window* window)
+    aura::Window* window)
     : window_(window),
       activate_button_(new TransparentActivateWindowButton(
           window_->GetRootWindow(), this)),
@@ -302,6 +317,34 @@ void ScopedTransformOverviewWindow::SetOpacity(float opacity) {
   }
 }
 
+void ScopedTransformOverviewWindow::Scroll(int delta_x) {
+  const float opacity = CalculateOpacityFromScrollDistance(delta_x);
+
+  ScopedOverviewAnimationSettings animation_settings(
+      OverviewAnimationType::SELECTOR_ITEM_SCROLL,
+      window());
+  gfx::Transform new_transform;
+  new_transform.Translate(delta_x, 0);
+  new_transform.PreconcatTransform(get_overview_transform());
+  SetTransform(window()->GetRootWindow(), new_transform);
+
+  SetOpacity(opacity);
+}
+
+void ScopedTransformOverviewWindow::CancelScroll() {
+  ScopedOverviewAnimationSettings animation_settings(
+    OverviewAnimationType::SELECTOR_ITEM_SCROLL_CANCEL,
+    window());
+
+  // The target opacity is set before the transform so that the
+  // WindowSelectorItem::OnWindowTransformed handler can properly
+  // update the opacity of the close button to the window's target
+  // opacity.
+  SetOpacity(1.0);
+  SetTransform(window()->GetRootWindow(),
+               get_overview_transform());
+}
+
 void ScopedTransformOverviewWindow::Select() {
   wm::GetWindowState(window_)->Activate();
 }