Add a .withAnnotation() method to simplify creating keys with different annotations.

Closes #1108

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=313246519

Author: kashike

core/src/com/google/inject/Key.java

@@ -290,6 +290,30 @@ public <T> Key<T> ofType(TypeLiteral<T> type) {
     return new Key<T>(type, annotationStrategy);
   }
 
+  /**
+   * Returns a new key of the same type with the specified annotation.
+   *
+   * <p>This is equivalent to {@code Key.get(key.getTypeLiteral(), annotation)} but may be more
+   * convenient to use in certain cases.
+   *
+   * @since vNext
+   */
+  public Key<T> withAnnotation(Class<? extends Annotation> annotationType) {
+    return new Key<T>(typeLiteral, strategyFor(annotationType));
+  }
+
+  /**
+   * Returns a new key of the same type with the specified annotation.
+   *
+   * <p>This is equivalent to {@code Key.get(key.getTypeLiteral(), annotation)} but may be more
+   * convenient to use in certain cases.
+   *
+   * @since vNext
+   */
+  public Key<T> withAnnotation(Annotation annotation) {
+    return new Key<T>(typeLiteral, strategyFor(annotation));
+  }
+
   /**
    * Returns true if this key has annotation attributes.
    *

core/test/com/google/inject/KeyTest.java

@@ -58,6 +58,23 @@ public void testOfType() {
     assertEquals(Foo.class, ki.getAnnotationType());
   }
 
+  public void testWithAnnotation() {
+    Key<Object> k = Key.get(Object.class);
+    Key<Object> kf = k.withAnnotation(Foo.class);
+    assertNull(k.getAnnotationType());
+    assertEquals(Foo.class, kf.getAnnotationType());
+  }
+
+  public void testWithAnnotationInstance() throws NoSuchFieldException {
+    Foo annotation = getClass().getDeclaredField("baz").getAnnotation(Foo.class);
+    Key<Object> k = Key.get(Object.class);
+    Key<Object> kf = k.withAnnotation(annotation);
+    assertNull(k.getAnnotationType());
+    assertNull(k.getAnnotation());
+    assertEquals(Foo.class, kf.getAnnotationType());
+    assertEquals(annotation, kf.getAnnotation());
+  }
+
   public void testKeyEquality() {
     Key<List<String>> a = new Key<List<String>>(Foo.class) {};
     Key<List<String>> b = Key.get(new TypeLiteral<List<String>>() {}, Foo.class);