src/vs/workbench/contrib/search/browser/searchView.ts/SearchView/trackInputBox
class SearchView:	private trackInputBox(inputFocusTracker: dom.IFocusTracker, contextKey?: IContextKey<boolean>): void {
		this._register(inputFocusTracker.onDidFocus(() => {
			this.lastFocusState = 'input';
			this.inputBoxFocused.set(true);
			if (contextKey) {
				contextKey.set(true);
			}
		}));
		this._register(inputFocusTracker.onDidBlur(() => {
			this.inputBoxFocused.set(this.searchWidget.searchInputHasFocus()
				|| this.searchWidget.replaceInputHasFocus()
				|| this.inputPatternIncludes.inputHasFocus()
				|| this.inputPatternExcludes.inputHasFocus());
			if (contextKey) {
				contextKey.set(false);
			}
		}));
	}