java - Chrome webdriver でページをズームアウトする方法

Question

次のコードでページをズームアウトしようとしました

driver.findElement(By.tagName("html")).sendKeys(Keys.chord(Keys.CONTROL, Keys.SUBTRACT));

これは Firefox Webdriver で正常に動作しています。しかし、Chromeでは機能しません。次の例外をスローします

org.openqa.selenium.WebDriverException: unknown error: cannot focus element
  (Session info: chrome=28.0.1500.71)
  (Driver info: chromedriver=2.3,platform=Linux 3.5.0-30-generic x86) (WARNING: The server did not provide any stacktrace information)
Command duration or timeout: 53 milliseconds
Build info: version: '2.37.0', revision: 'a7c61cb', time: '2013-10-18 17:15:02'
System info: host: 'vtiger-desktop', ip: '127.0.1.1', os.name: 'Linux', os.arch: 'i386', os.version: '3.5.0-30-generic', java.version: '1.7.0_12-ea'
Session ID: 918da5187e72caa1e68c49614c187dee
Driver info: org.openqa.selenium.chrome.ChromeDriver
Capabilities [{platform=LINUX, acceptSslCerts=true, javascriptEnabled=true, browserName=chrome, chrome={chromedriverVersion=2.3}, rotatable=false, locationContextEnabled=true, version=28.0.1500.71, cssSelectorsEnabled=true, databaseEnabled=true, handlesAlerts=true, browserConnectionEnabled=false, webStorageEnabled=true, nativeEvents=true, applicationCacheEnabled=false, takesScreenshot=true}]
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at org.openqa.selenium.remote.ErrorHandler.createThrowable(ErrorHandler.java:193)
    at org.openqa.selenium.remote.ErrorHandler.throwIfResponseFailed(ErrorHandler.java:145)
    at org.openqa.selenium.remote.RemoteWebDriver.execute(RemoteWebDriver.java:554)
    at org.openqa.selenium.remote.RemoteWebElement.execute(RemoteWebElement.java:268)
    at org.openqa.selenium.remote.RemoteWebElement.sendKeys(RemoteWebElement.java:89)