Fix calls to TreeScanner.scan(TreePath, param).

This is probably not what was intended: because TreePath implements Iterable<Tree>, this will scan from all nodes in the TreePath.
It don't think this is a problem in either case, because they only look to be called with a path referring to a CompilationUnitTree; but this is a bit brittle.

(An alternative fix would be to make these scanners into TreePathScanners. That TreeScanner and TreePathScanner do very different things with a TreePath parameter is quite insidious.

RELNOTES: None

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=228960415

core/src/main/java/com/google/errorprone/bugpatterns/Unused.java

@@ -213,7 +213,7 @@ public Description matchCompilationUnit(CompilationUnitTree tree, VisitorState s
     // We will skip reporting on the whole compilation if there are any native methods found.
     // Use a TreeScanner to find all local variables and fields.
     // The only reason type is atomic here is that we need to set its value from inside the closure.
-    if (hasNativeMethods(state.getPath())) {
+    if (hasNativeMethods(tree)) {
       // Skipping the analysis of this file because it has native methods.
       return Description.NO_MATCH;
     }
@@ -650,7 +650,7 @@ public Void visitMethodInvocation(MethodInvocationTree tree, Void unused) {
     return Description.NO_MATCH;
   }
 
-  private static boolean hasNativeMethods(TreePath path) {
+  private static boolean hasNativeMethods(CompilationUnitTree tree) {
     AtomicBoolean hasAnyNativeMethods = new AtomicBoolean(false);
     new TreeScanner<Void, Void>() {
       @Override
@@ -660,7 +660,7 @@ public Void visitMethod(MethodTree tree, Void unused) {
         }
         return null;
       }
-    }.scan(path, null);
+    }.scan(tree, null);
     return hasAnyNativeMethods.get();
   }
 

core/src/main/java/com/google/errorprone/refaster/RefasterRule.java

@@ -120,7 +120,8 @@ public abstract class RefasterRule<M extends TemplateMatch, T extends Template<M
   @Override
   public void apply(TreePath path, Context context, DescriptionListener listener) {
     RefasterScanner.create(this, listener)
-        .scan(path, prepareContext(context, (JCCompilationUnit) path.getCompilationUnit()));
+        .scan(
+            path.getLeaf(), prepareContext(context, (JCCompilationUnit) path.getCompilationUnit()));
   }
 
   boolean rejectMatchesWithComments() {