Remove temporary code in FullscreenController and WebWidgetClient.

Source/web/FullscreenController.cpp

Index: Source/web/FullscreenController.cpp
diff --git a/Source/web/FullscreenController.cpp b/Source/web/FullscreenController.cpp
index 3c149a94dbe07f9edfd1a3ccac53040c5d242b29..9d493cf85262440595aacd9ced2131d2b5abf4e2 100644
--- a/Source/web/FullscreenController.cpp
+++ b/Source/web/FullscreenController.cpp
@@ -38,8 +38,8 @@
 #include "core/html/HTMLVideoElement.h"
 #include "platform/LayoutTestSupport.h"
 #include "platform/RuntimeEnabledFeatures.h"
+#include "public/platform/WebLayerTreeView.h"
 #include "public/web/WebFrameClient.h"
-#include "public/web/WebViewClient.h"
 #include "web/WebLocalFrameImpl.h"
 #include "web/WebSettingsImpl.h"
 #include "web/WebViewImpl.h"
@@ -147,14 +147,10 @@ void FullscreenController::enterFullScreenForElement(Element* element)
     }
 
     // We need to transition to fullscreen mode.
-    // FIXME: temporarily try to use WebFrameClient and WebViewClient while
-    // Chromium switches from one to the other, see https://crbug.com/374854
     WebLocalFrameImpl* frame = WebLocalFrameImpl::fromFrame(element->document().frame());
-    if (frame && frame->client() && frame->client()->enterFullscreen()) {
+    if (frame && frame->client()) {
+        frame->client()->enterFullscreen();
         m_provisionalFullScreenElement = element;
-    } else if (WebViewClient* client = m_webViewImpl->client()) {
-        if (client->enterFullScreen())
-            m_provisionalFullScreenElement = element;
     }
 }
 
@@ -164,14 +160,9 @@ void FullscreenController::exitFullScreenForElement(Element* element)
     if (m_isCancelingFullScreen)
         return;
 
-    // FIXME: temporarily try to use WebFrameClient and WebViewClient while
-    // Chromium switches from one to the other, see https://crbug.com/374854
     WebLocalFrameImpl* frame = WebLocalFrameImpl::fromFrame(element->document().frame());
-    if (frame && frame->client() && frame->client()->exitFullscreen())
-        return;
-
-    if (WebViewClient* client = m_webViewImpl->client())
-        client->exitFullScreen();
+    if (frame && frame->client())
+        frame->client()->exitFullscreen();
 }
 
 void FullscreenController::updateSize()