[blimp] Add support for having multiple tabs

blimp/engine/session/blimp_engine_session.h

Index: blimp/engine/session/blimp_engine_session.h
diff --git a/blimp/engine/session/blimp_engine_session.h b/blimp/engine/session/blimp_engine_session.h
index 5c363bb488beec9b45c9273244ba6c61febe24e7..0b8c91f461415e75afa4e5e8f78df4a0ec8f656c 100644
--- a/blimp/engine/session/blimp_engine_session.h
+++ b/blimp/engine/session/blimp_engine_session.h
@@ -72,11 +72,9 @@ class BlimpWindowTreeHost;
 class EngineNetworkComponents;
 class Tab;
 
-class BlimpEngineSession
-    : public BlimpMessageProcessor,
-      public content::WebContentsDelegate,
-      public ui::InputMethodObserver,
-      public EngineRenderWidgetFeature::RenderWidgetMessageDelegate {
+class BlimpEngineSession : public BlimpMessageProcessor,
+                           public content::WebContentsDelegate,
+                           public ui::InputMethodObserver {
  public:
   using GetPortCallback = base::Callback<void(uint16_t)>;
 
@@ -124,15 +122,6 @@ class BlimpEngineSession
   // |device_pixel_ratio|.
   void HandleResize(float device_pixel_ratio, const gfx::Size& size);
 
-  // RenderWidgetMessage handler methods.
-  // RenderWidgetMessageDelegate implementation.
-  void OnWebGestureEvent(
-      content::RenderWidgetHost* render_widget_host,
-      std::unique_ptr<blink::WebGestureEvent> event) override;
-  void OnCompositorMessageReceived(
-      content::RenderWidgetHost* render_widget_host,
-      const std::vector<uint8_t>& message) override;
-
   // content::WebContentsDelegate implementation.
   content::WebContents* OpenURLFromTab(
       content::WebContents* source,