Using the chromium clearView implementation

Landed upstream in:
https://codereview.chromium.org/22849016/

Fix for bug 5012842

Change-Id: I74e2822bb41ba4fb6f6b73248bef52d423c7903b
diff --git a/chromium/java/com/android/webview/chromium/WebViewChromium.java b/chromium/java/com/android/webview/chromium/WebViewChromium.java
index e52ef02..061eb27 100644
--- a/chromium/java/com/android/webview/chromium/WebViewChromium.java
+++ b/chromium/java/com/android/webview/chromium/WebViewChromium.java
@@ -710,7 +710,7 @@
             });
             return;
         }
-        UnimplementedWebViewApi.invoke();
+        mAwContents.clearView();
     }
 
     @Override