Add power-user keyboard mode for ChromeOS with Search key acting as a typical Fn 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 f6199cc4e3024597da006da8b2c15bc9c4db337e..7f94f3b172430cb797b2ab6e17efd8f4534801a0 100644
--- a/ash/accelerators/accelerator_controller.cc
+++ b/ash/accelerators/accelerator_controller.cc
@@ -534,6 +534,31 @@ bool AcceleratorController::PerformAction(int action,
       // this key combination is reserved for partial screenshot.
       return true;
     case TOGGLE_APP_LIST:
+      if (accelerator.key_code() == ui::VKEY_LWIN) {
+        // For bindings on the Search key, activate the binding on press if the
+        // Search key is not acting as a modifier. Otherwise, activate it on
+        // release.
+
+        const ui::KeyboardCode previous_key_code =
+            context_.previous_accelerator().key_code();
+
+        const bool search_as_function_key =
+            Shell::GetInstance()->delegate()->IsSearchKeyActingAsFunctionKey();
+        const bool type_pressed = accelerator.type() == ui::ET_KEY_PRESSED;
+
+        if (!search_as_function_key && !type_pressed)
+          return false;
+        if (search_as_function_key && type_pressed)
+          return false;
+        if (search_as_function_key &&
+            // If something else was pressed between the Search key (LWIN)
+            // being pressed and released, then ignore the release of the
+            // Search key.
+            (previous_event_type == ui::ET_KEY_RELEASED ||
+             previous_key_code != ui::VKEY_LWIN)) {
+          return false;
+        }
+      }
       if (key_code == ui::VKEY_LWIN && shell->delegate())
         shell->delegate()->RecordUserMetricsAction(UMA_ACCEL_SEARCH_LWIN);
       // When spoken feedback is enabled, we should neither toggle the list nor