[theme] remove theme user setting when selecting default

src/vs/workbench/services/themes/electron-browser/themeService.ts

@@ -330,7 +330,7 @@ export class ThemeService implements IThemeService {
 		return this.onFileIconThemeChange.event;
 	}
 
-	private initialize(): TPromise<void> {
+	private initialize(): TPromise<any> {
 
 		let legacyColorThemeId = this.storageService.get('workbench.theme', StorageScope.GLOBAL, null);
 		let legacyIconThemeId = this.storageService.get('workbench.iconTheme', StorageScope.GLOBAL, null);
@@ -407,7 +407,11 @@ export class ThemeService implements IThemeService {
 
 	private writeColorThemeConfiguration(settingsTarget: ConfigurationTarget) {
 		if (!types.isUndefinedOrNull(settingsTarget)) {
-			return this.configurationEditingService.writeConfiguration(settingsTarget, { key: COLOR_THEME_SETTING, value: this.currentColorTheme.settingsId }).then(_ => {
+			let value = this.currentColorTheme.settingsId;
+			if (settingsTarget === ConfigurationTarget.USER && this.currentColorTheme.id === DEFAULT_THEME_ID) {
+				value = void 0; // remove key from user settings
+			}
+			return this.configurationEditingService.writeConfiguration(settingsTarget, { key: COLOR_THEME_SETTING, value }).then(_ => {
 				return this.currentColorTheme;
 			});
 		}
@@ -606,7 +610,11 @@ export class ThemeService implements IThemeService {
 
 	private writeFileIconConfiguration(settingsTarget: ConfigurationTarget): TPromise<IFileIconTheme> {
 		if (!types.isUndefinedOrNull(settingsTarget)) {
-			return this.configurationEditingService.writeConfiguration(settingsTarget, { key: ICON_THEME_SETTING, value: this.currentIconTheme.settingsId }).then(_ => {
+			let value = this.currentIconTheme.settingsId;
+			if (settingsTarget === ConfigurationTarget.USER && this.currentIconTheme.id === '') {
+				value = void 0; // remove key from user settings
+			}
+			return this.configurationEditingService.writeConfiguration(settingsTarget, { key: ICON_THEME_SETTING, value }).then(_ => {
 				return this.currentIconTheme;
 			});
 		}