Support dragging texts out of webview/Chrome.

content/browser/web_contents/web_contents_view_android.cc

 // Copyright (c) 2012 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 "content/browser/web_contents/web_contents_view_android.h"
 
 #include "base/logging.h"
 #include "content/browser/android/content_view_core_impl.h"
 #include "content/browser/frame_host/interstitial_page_impl.h"
 #include "content/browser/renderer_host/render_widget_host_view_android.h"
@@ skipping 176 matching lines @@
   if (content_view_core_)
     content_view_core_->HideSelectPopupMenu();
 }
 
 void WebContentsViewAndroid::StartDragging(
     const DropData& drop_data,
     blink::WebDragOperationsMask allowed_ops,
     const gfx::ImageSkia& image,
     const gfx::Vector2d& image_offset,
     const DragEventSourceInfo& event_info) {
-  NOTIMPLEMENTED();
+  if (drop_data.text.is_null())
+    return;
+  base::string16 dragged_text = drop_data.text.string();
+  content_view_core_->StartDragging(dragged_text, image);
 }
 
 void WebContentsViewAndroid::UpdateDragCursor(blink::WebDragOperation op) {
   // Intentional no-op because Android does not have cursor.
 }
 
 void WebContentsViewAndroid::OnDragEntered(
     const std::vector<DropData::Metadata>& metadata,
     const gfx::Point& location,
     const gfx::Point& screen_location) {
+  blink::WebDragOperationsMask allowed_ops =
+      static_cast<blink::WebDragOperationsMask>(blink::WebDragOperationCopy |
+                                                blink::WebDragOperationMove);

[dcheng, 2016/07/08 06:30:30]

Out of curiosity, why did we change this from Copy to Copy+Move?

[hush (inactive), 2016/07/08 18:23:24]

The move operation is to support dragging texts within the same chrome tab or
the same webview. Android TextView does this too: when you drag within the same
view, it's gonna be a move, otherwise a copy.

So if I don't allow move here, WebViewImpl::dragTargetDrop will just early out
(because blink wants to move the text but wasn't allowed to do so, as a result,
m_dragOperation in WebViewImpl is set to WebDragOperationNone)
See here
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/web/WebViewImp...

   web_contents_->GetRenderViewHost()->DragTargetDragEnterWithMetaData(
-      metadata, location, screen_location, blink::WebDragOperationCopy, 0);
+      metadata, location, screen_location, allowed_ops, 0);
 }
 
 void WebContentsViewAndroid::OnDragUpdated(const gfx::Point& location,
                                            const gfx::Point& screen_location) {
+  blink::WebDragOperationsMask allowed_ops =
+      static_cast<blink::WebDragOperationsMask>(blink::WebDragOperationCopy |
+                                                blink::WebDragOperationMove);
   web_contents_->GetRenderViewHost()->DragTargetDragOver(
-      location, screen_location, blink::WebDragOperationCopy, 0);
+      location, screen_location, allowed_ops, 0);
 }
 
 void WebContentsViewAndroid::OnDragExited() {
   web_contents_->GetRenderViewHost()->DragTargetDragLeave();
 }
 
 void WebContentsViewAndroid::OnPerformDrop(DropData* drop_data,
                                            const gfx::Point& location,
                                            const gfx::Point& screen_location) {
   web_contents_->GetRenderViewHost()->FilterDropData(drop_data);
   web_contents_->GetRenderViewHost()->DragTargetDrop(*drop_data, location,
                                                      screen_location, 0);
 }
 
+void WebContentsViewAndroid::OnDragEnded() {
+  web_contents_->GetRenderViewHost()->DragSourceSystemDragEnded();
+}
+
 void WebContentsViewAndroid::GotFocus() {
   // This is only used in the views FocusManager stuff but it bleeds through
   // all subclasses. http://crbug.com/21875
 }
 
 // This is called when we the renderer asks us to take focus back (i.e., it has
 // iterated past the last focusable element on the page).
 void WebContentsViewAndroid::TakeFocus(bool reverse) {
   if (web_contents_->GetDelegate() &&
       web_contents_->GetDelegate()->TakeFocus(web_contents_, reverse))
     return;
   web_contents_->GetRenderWidgetHostView()->Focus();
 }
 
 } // namespace content