Add window overview mode behind --ash-enable-overview-mode flag to F5 key.

ash/accelerators/accelerator_controller.cc

Index: ash/accelerators/accelerator_controller.cc
diff --git a/ash/accelerators/accelerator_controller.cc b/ash/accelerators/accelerator_controller.cc
index b96c201cf62b92d68d3105f0f5a93ca84cb4fdde..19fba850bae85366c0a53920e97cd500cbb3e63b 100644
--- a/ash/accelerators/accelerator_controller.cc
+++ b/ash/accelerators/accelerator_controller.cc
@@ -95,7 +95,11 @@ bool HandleCycleWindowMRU(WindowCycleController::Direction direction,
 
 void HandleCycleWindowLinear(CycleDirection direction) {
   Shell::GetInstance()->
-        window_cycle_controller()->HandleLinearCycleWindow();
+      window_cycle_controller()->HandleLinearCycleWindow();
+}
+
+void ToggleOverviewMode() {
+  Shell::GetInstance()->window_cycle_controller()->ToggleOverview();
 }
 
 bool HandleAccessibleFocusCycle(bool reverse) {
@@ -521,11 +525,23 @@ bool AcceleratorController::PerformAction(int action,
       return HandleCycleWindowMRU(WindowCycleController::FORWARD,
                                   accelerator.IsAltDown());
     case CYCLE_BACKWARD_LINEAR:
+      if (CommandLine::ForCurrentProcess()->HasSwitch(
+              switches::kAshEnableOverviewMode)) {
+        shell->delegate()->RecordUserMetricsAction(UMA_ACCEL_OVERVIEW_F5);
+        ToggleOverviewMode();
+        return true;
+      }
       if (key_code == ui::VKEY_MEDIA_LAUNCH_APP1)
         shell->delegate()->RecordUserMetricsAction(UMA_ACCEL_PREVWINDOW_F5);
       HandleCycleWindowLinear(CYCLE_BACKWARD);
       return true;
     case CYCLE_FORWARD_LINEAR:
+      if (CommandLine::ForCurrentProcess()->HasSwitch(
+              switches::kAshEnableOverviewMode)) {
+        shell->delegate()->RecordUserMetricsAction(UMA_ACCEL_OVERVIEW_F5);
+        ToggleOverviewMode();
+        return true;
+      }
       if (key_code == ui::VKEY_MEDIA_LAUNCH_APP1)
         shell->delegate()->RecordUserMetricsAction(UMA_ACCEL_NEXTWINDOW_F5);
       HandleCycleWindowLinear(CYCLE_FORWARD);