Isolate plugin class directories from each other

Configure Eclipse to compile/copy each plugin's classes and resources
into its own private classes folder.  This should fix the duplicate
resource warnings for about.md or other documentation and static image
assets.

Move test and utility classes into their own directories too. This
has no real impact on the runtime classpath at this time, but opens
the door to do something more creative later.

Change-Id: If2a048dfe0349f671a17f9e80d6f22a69a5c0ade

gerrit-launcher/src/main/java/com/google/gerrit/launcher/GerritLauncher.java

@@ -556,6 +556,50 @@ public final class GerritLauncher {
     }
   }
 
+  /**
+   * Locate the path of the {@code buck-out} directory in a source tree.
+   *
+   * @throws FileNotFoundException if the directory cannot be found.
+   */
+  public static File getDeveloperBuckOut() throws FileNotFoundException {
+    // Find ourselves in the CLASSPATH, we should be a loose class file.
+    Class<GerritLauncher> self = GerritLauncher.class;
+    URL u = self.getResource(self.getSimpleName() + ".class");
+    if (u == null) {
+      throw new FileNotFoundException("Cannot find class " + self.getName());
+    } else if (!"file".equals(u.getProtocol())) {
+      throw new FileNotFoundException("Cannot find extract path from " + u);
+    }
+
+    // Pop up to the top level classes folder that contains us.
+    File dir = new File(u.getPath());
+    String myName = self.getName();
+    for (;;) {
+      int dot = myName.lastIndexOf('.');
+      if (dot < 0) {
+        dir = dir.getParentFile();
+        break;
+      }
+      myName = myName.substring(0, dot);
+      dir = dir.getParentFile();
+    }
+
+    dir = popdir(u, dir, "classes");
+    dir = popdir(u, dir, "eclipse");
+    if ("buck-out".equals(dir.getName())) {
+      return dir;
+    }
+    throw new FileNotFoundException("Cannot find buck-out from " + u);
+  }
+
+  private static File popdir(URL u, File dir, String name)
+      throws FileNotFoundException {
+    if (dir.getName().equals(name)) {
+      return dir.getParentFile();
+    }
+    throw new FileNotFoundException("Cannot find buck-out from " + u);
+  }
+
   private GerritLauncher() {
   }
 }