[Fuchsia] Migrate FIDL from "interface" to "protocol" syntax.

Bug: 931860
Change-Id: I8c7beaf359bf192d299ba730ae40971ad66c5932
Reviewed-on: https://chromium-review.googlesource.com/c/1471262
Auto-Submit: Wez <wez@chromium.org>
Reviewed-by: Fabrice de Gans-Riberi <fdegans@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#631958}

base/fuchsia/test.fidl

@@ -5,6 +5,6 @@
 library base.fuchsia.testfidl;
 
 [Discoverable]
-interface TestInterface {
+protocol TestInterface {
   Add(int32 a, int32 b) -> (int32 sum);
 };

build/fuchsia/fidlgen_js/test/simple.fidl

@@ -100,11 +100,11 @@ struct AfterPreviousReference {
   int32 an_int;
 };
 
-interface AnotherInterface {
+protocol AnotherInterface {
   TimesTwo(int32 a) -> (int32 b);
 };
 
-interface Testola {
+protocol Testola {
   DoSomething();
 
   PrintInt(int32 num);

fuchsia/fidl/cast/application_config.fidl

@@ -18,7 +18,7 @@ struct ApplicationConfig {
 
 /// Service interface for working with application configurations.
 [Discoverable]
-interface ApplicationConfigManager {
+protocol ApplicationConfigManager {
   /// Returns the ApplicationConfig for the specified application Id.
   GetConfig(string id) -> (ApplicationConfig? config);
 };

fuchsia/fidl/cast/cast_channel.fidl

@@ -7,7 +7,7 @@ library chromium.cast;
 using chromium.web;
 
 [Discoverable]
-interface CastChannel {
+protocol CastChannel {
   /// Receives an opened Cast |channel| from the Cast application.
   /// The return callback is invoked when the service is ready to accept a new
   /// Cast Channel. OnOpened() should not be called again until this happens.

fuchsia/fidl/web/context.fidl

@@ -6,7 +6,7 @@ library chromium.web;
 
 /// Manages browsing state (e.g. LocalStorage, cookies, etc) associated with
 /// a set of Frames.
-interface Context {
+protocol Context {
   /// Creates a new frame under this Context.
   ///
   /// |frame|: An interface request that will be bound to the created Frame.

fuchsia/fidl/web/context_provider.fidl

@@ -7,7 +7,7 @@ library chromium.web;
 /// The top-level service interface which allows for the creation of
 /// Context resources.
 [Discoverable]
-interface ContextProvider {
+protocol ContextProvider {
   /// Creates a new browser Context whose state is wholly independent and
   /// isolated from other Contexts.
   ///

fuchsia/fidl/web/frame.fidl

@@ -28,7 +28,7 @@ enum LogLevel : int32 {
   ERROR = 2;
 };
 
-interface Frame {
+protocol Frame {
   /// Creates a new view using the specified |view_token|. Caller should pass
   /// the other end of the token to CreateViewHolderCmd() to attach the new view
   /// to a the view tree.
@@ -123,7 +123,7 @@ union IncomingTransferable {
 /// and exchange Messages with the peered MessagePort in the Frame's script
 /// context. The port is destroyed when either end of the MessagePort channel
 /// is torn down.
-interface MessagePort {
+protocol MessagePort {
   /// Sends a WebMessage to the peer.
   PostMessage(WebMessage message) -> (bool success);
 

fuchsia/fidl/web/navigation_controller.fidl

@@ -6,7 +6,7 @@ library chromium.web;
 
 /// Provides methods for controlling and querying the navigation state
 /// of a Frame.
-interface NavigationController {
+protocol NavigationController {
   /// Tells the Frame to navigate to a |url|.
   ///
   /// |url|:    The address to navigate to.

fuchsia/fidl/web/navigation_event_observer.fidl

@@ -15,7 +15,7 @@ struct NavigationEvent {
 
 /// Interface supplied by the embedder for receiving notifications about
 /// navigation events in a Frame.
-interface NavigationEventObserver {
+protocol NavigationEventObserver {
   /// Called when user-visible navigation state has changed since Frame
   /// creation or the last acknowledgement callback, whichever occurred later.
   /// |change| will contain all the differences in navigation state since the