Explain why ExpectedCondition continues to extend guava's Function

It's to avoid having users rewrite code. We're so
dependent on the library it doesn't make sense to
remove a single call site.

java/client/src/org/openqa/selenium/support/ui/ExpectedCondition.java

@@ -32,4 +32,7 @@
  *
  * @param <T> The return type
  */
+// NB: this originally extended Guava's Function interface since Java didn't have one. To avoid code
+// such as "com.google.common.base.Function condition = ExpectedConditions.elementFound(By);"
+// breaking at compile time, we continue to extend Guava's Function interface.
 public interface ExpectedCondition<T> extends Function<WebDriver, T> {}