Update Javadoc references from gcm to fcm.

Author: gsakakihara

firebase-messaging/src/main/java/com/google/firebase/messaging/Constants.java

@@ -107,7 +107,7 @@ public static final class MessagePayloadKeys {
     /**
      * Prefix "google.c" for keys that are reserved for the client library. While all the other
      * "google." are removed at GmsCore level, google.c keys are preserved in the intent extras, and
-     * should be removed by the Gcm Client Library, before passing the user data to the app.
+     * should be removed by the FCM Client Library, before passing the user data to the app.
      */
     public static final String RESERVED_CLIENT_LIB_PREFIX = RESERVED_PREFIX + "c.";
 

firebase-messaging/src/main/java/com/google/firebase/messaging/FirebaseMessaging.java

@@ -71,7 +71,7 @@
  *
  * <pre>
  * FirebaseMessaging.getInstance().send(
- *     new RemoteMessage.Builder(SENDER_ID + "&#64;gcm.googleapis.com")
+ *     new RemoteMessage.Builder(SENDER_ID + "&#64;fcm.googleapis.com")
  *     .setMessageId(id)
  *     .addData("key", "value")
  *     .build());</pre>

firebase-messaging/src/main/java/com/google/firebase/messaging/MessagingAnalytics.java

@@ -43,7 +43,7 @@
 import java.util.concurrent.ExecutionException;
 
 /**
- * Provides integration between GCM and Scion.
+ * Provides integration between FCM and Scion.
  *
  * <p>All Scion dependencies should be kept in this class, and missing dependencies should be
  * handled gracefully. Instead of crashing the app if Scion has not been included in the APK we

firebase-messaging/src/main/java/com/google/firebase/messaging/RemoteMessage.java

@@ -116,7 +116,7 @@ public String getFrom() {
    * Gets the message destination.
    *
    * <ul>
-   *   <li>For upstream messages, this will be of the form {@code SENDER_ID@gcm.googleapis.com}.
+   *   <li>For upstream messages, this will be of the form {@code SENDER_ID@fcm.googleapis.com}.
    *   <li>For downstream messages, this will be the Firebase installations ID (FID).
    * </ul>
    */
@@ -298,7 +298,7 @@ public static class Builder {
      * Sets the destination of the message.
      *
      * @param to The destination of the message in the format of {@code
-     *     SENDER_ID@gcm.googleapis.com}. The {@code SENDER_ID} should be the FirebaseApp gcm sender
+     *     SENDER_ID@fcm.googleapis.com}. The {@code SENDER_ID} should be the FirebaseApp gcm sender
      *     id.
      */
     public Builder(@NonNull String to) {