Make ABI change mutators more robust

We add a reference to the newly added method into one
of the existing methods. This would fail if the existing
method was static, because our newly added method was an
instance method. Fixed by making that method static too.

.gitignore

@@ -5,4 +5,6 @@ classes
 /profile-out
 /profile-out-*
 /foobar
-/gradle-user-home
+/gradle-user-home
+/out
+.DS_STORE

src/main/java/org/gradle/profiler/mutations/ApplyAbiChangeToJavaSourceFileMutator.java

@@ -31,6 +31,6 @@ protected void applyChangeTo(CompilationUnit compilationUnit) {
         MethodDeclaration existingMethod = methods.get(0);
         existingMethod.getBody().get().addStatement(0, new MethodCallExpr(null, newMethodName));
 
-        type.addMethod(newMethodName, Modifier.PUBLIC);
+        type.addMethod(newMethodName, Modifier.PUBLIC, Modifier.STATIC);
     }
 }

src/test/groovy/org/gradle/profiler/mutations/ApplyAbiChangeToJavaSourceFileMutatorTest.groovy

@@ -19,19 +19,19 @@ class ApplyAbiChangeToJavaSourceFileMutatorTest extends Specification {
         mutator.beforeBuild()
 
         then:
-        parse(sourceFile) == parse("class Thing { public void existingMethod() { _m_1234_1();}public void _m_1234_1() { }}")
+        parse(sourceFile) == parse("class Thing { public void existingMethod() { _m_1234_1();}public static void _m_1234_1() { }}")
 
         when:
         mutator.beforeBuild()
 
         then:
-        parse(sourceFile) == parse("class Thing { public void existingMethod() { _m_1234_2();}public void _m_1234_2() { }}")
+        parse(sourceFile) == parse("class Thing { public void existingMethod() { _m_1234_2();}public static void _m_1234_2() { }}")
 
         when:
         mutator.beforeBuild()
 
         then:
-        parse(sourceFile) == parse("class Thing { public void existingMethod() { _m_1234_3();}public void _m_1234_3() { }}")
+        parse(sourceFile) == parse("class Thing { public void existingMethod() { _m_1234_3();}public static void _m_1234_3() { }}")
     }
 
     def "reverts changes when nothing has been applied"() {