[file-history] shorten wait time for synchronous diff loading in preview

This allows to walk through the history graph faster.

platform/diff-impl/src/com/intellij/diff/impl/CacheDiffRequestProcessor.java

@@ -117,10 +117,14 @@ public abstract class CacheDiffRequestProcessor<T> extends DiffRequestProcessor
       () -> {
         applyRequest(new LoadingDiffRequest(getRequestName(requestProvider)), force, scrollToChangePolicy);
       },
-      ProgressWindow.DEFAULT_PROGRESS_DIALOG_POSTPONE_TIME_MILLIS
+      getFastLoadingTimeMillis()
     );
   }
 
+  protected int getFastLoadingTimeMillis() {
+    return ProgressWindow.DEFAULT_PROGRESS_DIALOG_POSTPONE_TIME_MILLIS;
+  }
+
   @Nullable
   protected DiffRequest loadRequestFast(@NotNull T provider) {
     return myRequestCache.get(provider);

platform/vcs-log/impl/src/com/intellij/vcs/log/history/FileHistoryDiffPreview.kt

@@ -38,6 +38,10 @@ internal class FileHistoryDiffPreview(project: Project, private val changeGetter
     }
   }
 
+  override fun getFastLoadingTimeMillis(): Int {
+    return 10
+  }
+
   private inner class MyChangeWrapper internal constructor(private val change: Change) : ChangeViewDiffRequestProcessor.Wrapper() {
 
     override fun getUserObject(): Any {