[diff]: move toggle diff preview action into separated class

platform/vcs-impl/src/com/intellij/openapi/vcs/changes/ChangesViewManager.java

@@ -43,6 +43,7 @@ import com.intellij.openapi.vcs.VcsBundle;
 import com.intellij.openapi.vcs.VcsConfiguration;
 import com.intellij.openapi.vcs.VcsException;
 import com.intellij.openapi.vcs.changes.actions.IgnoredSettingsAction;
+import com.intellij.openapi.vcs.changes.actions.ShowDiffPreviewAction;
 import com.intellij.openapi.vcs.changes.shelf.ShelveChangesManager;
 import com.intellij.openapi.vcs.changes.ui.*;
 import com.intellij.openapi.vfs.VirtualFile;
@@ -474,27 +475,13 @@ public class ChangesViewManager implements ChangesViewI, ProjectComponent, Persi
     }
   }
 
-  private class ToggleDetailsAction extends ToggleAction implements DumbAware {
-    private ToggleDetailsAction() {
-      super("Preview Diff", null, AllIcons.Actions.DiffPreview);
-    }
-
-    @Override
-    public boolean isSelected(AnActionEvent e) {
-      return assertNotNull(mySplitterComponent).isDetailsOn();
-    }
-
+  private class ToggleDetailsAction extends ShowDiffPreviewAction {
     @Override
     public void setSelected(AnActionEvent e, boolean state) {
+      super.setSelected(e, state);
       assertNotNull(mySplitterComponent).setDetailsOn(state);
       VcsConfiguration.getInstance(myProject).LOCAL_CHANGES_DETAILS_PREVIEW_SHOWN = state;
     }
-
-    @Override
-    public void update(@NotNull AnActionEvent e) {
-      super.update(e);
-      e.getPresentation().setEnabled(mySplitterComponent != null);
-    }
   }
 
   private class MyChangeProcessor extends CacheChangeProcessor {

platform/vcs-impl/src/com/intellij/openapi/vcs/changes/actions/ShowDiffPreviewAction.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2000-2017 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.intellij.openapi.vcs.changes.actions;
+
+import com.intellij.icons.AllIcons;
+import com.intellij.openapi.actionSystem.AnActionEvent;
+import com.intellij.openapi.actionSystem.ToggleAction;
+import com.intellij.openapi.project.DumbAware;
+
+public abstract class ShowDiffPreviewAction extends ToggleAction implements DumbAware {
+  private boolean myState;
+
+  public ShowDiffPreviewAction() {
+    super("Preview Diff", null, AllIcons.Actions.DiffPreview);
+  }
+
+  @Override
+  public boolean isSelected(AnActionEvent e) {
+    return myState;
+  }
+
+  @Override
+  public void setSelected(AnActionEvent e, boolean state) {
+    myState = state;
+  }
+}