Use instance equality for Context.Key

This allows applications to limit the visibility of values simply by not
exposing the Key instance being used.

core/src/main/java/io/grpc/Context.java

@@ -160,14 +160,16 @@ public class Context {
   };
 
   /**
-   * Create a {@link Key} with the given name.
+   * Create a {@link Key} with the given debug name. Multiple different keys may have the same name;
+   * the name is intended for debugging purposes and does not impact behavior.
    */
   public static <T> Key<T> key(String name) {
     return new Key<T>(name);
   }
 
   /**
-   * Create a {@link Key} with the given name and default value.
+   * Create a {@link Key} with the given debug name and default value. Multiple different keys may
+   * have the same name; the name is intended for debugging purposes and does not impact behavior.
    */
   public static <T> Key<T> keyWithDefault(String name, T defaultValue) {
     return new Key<T>(name, defaultValue);
@@ -768,25 +770,6 @@ public class Context {
       return value == null ? defaultValue : value;
     }
 
-    @Override
-    public boolean equals(Object o) {
-      if (this == o) {
-        return true;
-      }
-      if (o == null || getClass() != o.getClass()) {
-        return false;
-      }
-
-      Key<?> key = (Key<?>) o;
-
-      return key.name.equals(this.name);
-    }
-
-    @Override
-    public int hashCode() {
-      return name.hashCode();
-    }
-
     @Override
     public String toString() {
       return name;

core/src/test/java/io/grpc/ContextTest.java

@@ -711,12 +711,12 @@ public class ContextTest {
   @Test
   public void testKeyEqualsHashCode() {
     assertTrue(PET.equals(PET));
-    assertTrue(PET.equals(Context.key("pet")));
+    assertFalse(PET.equals(Context.key("pet")));
     assertFalse(PET.equals(FOOD));
     assertFalse(PET.equals("pet"));
     assertFalse(PET.equals(null));
 
-    assertEquals(PET.hashCode(), Context.key("pet").hashCode());
+    assertEquals(PET.hashCode(), PET.hashCode());
   }
 
   private static class QueuedExecutor implements Executor {