We have two copies of the ObservableList.java class in our source tree:

modules/base/src/main/java7/javafx/collections/ObservableList.java
modules/base/src/main/java8/javafx/collections/ObservableList.java

We should remove modules/base/src/main/java7 and move the java8 version of this class from modules/base/src/main/java8/javafx/collections/ObservableList.java to modules/base/src/main/java/javafx/collections/ (using "hg mv" so it is tracked as a rename). We should then remove any references to src/main/java7 and src/main/java8 from build.gradle.

This will avoid some special-case logic when we start building javafx with a JIGSAW-based compiler.