Disable WebView/Chrome's drag and drop feature on M and below.

ui/android/view_android.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/android/view_android.h"
 
 #include <algorithm>
 
 #include "base/android/jni_android.h"
 #include "cc/layers/layer.h"
@@ skipping 146 matching lines @@
 }
 
 cc::Layer* ViewAndroid::GetLayer() const {
   return layer_.get();
 }
 
 void ViewAndroid::SetLayer(scoped_refptr<cc::Layer> layer) {
   layer_ = layer;
 }
 
-void ViewAndroid::StartDragAndDrop(const JavaRef<jstring>& jtext,
+bool ViewAndroid::StartDragAndDrop(const JavaRef<jstring>& jtext,
                                    const JavaRef<jobject>& jimage) {
   ScopedJavaLocalRef<jobject> delegate(GetViewAndroidDelegate());
   if (delegate.is_null())
-    return;
+    return false;
   JNIEnv* env = base::android::AttachCurrentThread();
-  Java_ViewAndroidDelegate_startDragAndDrop(env, delegate, jtext, jimage);
+  return Java_ViewAndroidDelegate_startDragAndDrop(env, delegate, jtext,
+                                                   jimage);
 }
 
 }  // namespace ui