Support dragging texts into Android WebView.

android_webview/java/src/org/chromium/android_webview/AwContents.java

Index: android_webview/java/src/org/chromium/android_webview/AwContents.java
diff --git a/android_webview/java/src/org/chromium/android_webview/AwContents.java b/android_webview/java/src/org/chromium/android_webview/AwContents.java
index a710d513896e2f65cc45be90c0a0c6231c552b5f..681844751cb0e2bca6e2de5af54947ad015857e9 100644
--- a/android_webview/java/src/org/chromium/android_webview/AwContents.java
+++ b/android_webview/java/src/org/chromium/android_webview/AwContents.java
@@ -6,6 +6,7 @@ package org.chromium.android_webview;
 
 import android.annotation.SuppressLint;
 import android.app.Activity;
+import android.content.ClipDescription;
 import android.content.ComponentCallbacks2;
 import android.content.Context;
 import android.content.Intent;
@@ -2974,8 +2975,30 @@ public class AwContents implements SmartClipProvider,
 
         @Override
         public boolean onDragEvent(DragEvent event) {
-            // TODO(hush): implement this. crbug.com/584789
-            return false;
+            switch (event.getAction()) {
+                case DragEvent.ACTION_DRAG_STARTED:
+                    ClipDescription clipDescription = event.getClipDescription();

[Ted C, 2016/02/25 18:38:53]

I don't see any reason why we need to increase the api surface of
ContentViewCore beyond onDragEvent.  In particular, why doesn't this all live
within that class?

[hush (inactive), 2016/02/27 01:46:13]

No particular reason in fact. During the first draft, I was just being lazy and
trying to avoid creating a native counterpart class for DragEvent (just like
what we do for MotionEvent)

Anyway, I will do as you asked.

+                    // TODO(hush): support dragging more than just text.
+                    return clipDescription.hasMimeType(ClipDescription.MIMETYPE_TEXT_HTML)
+                            || clipDescription.hasMimeType(clipDescription.MIMETYPE_TEXT_PLAIN);
+                case DragEvent.ACTION_DRAG_ENTERED:
+                    mContentViewCore.onDragEntered(event);
+                    return true;
+                case DragEvent.ACTION_DRAG_LOCATION:
+                    mContentViewCore.onDragUpdated(event);
+                    return true;
+                case DragEvent.ACTION_DROP:
+                    // TODO(hush): onPerformDrop should return false when the receiving object does

[aelias_OOO_until_Jul13, 2016/02/25 20:58:00]

I don't think this one should be left as a TODO, since it just has to do with
simple text dragging.  It looks like the ContentViewCore methods (and below)
should plumb a boolean up to the code that decides to accept or reject.

Alternatively, is there even any concept in Chromium/HTML of rejecting a
drag-and-drop?  If not, this TODO should just be deleted.

[hush (inactive), 2016/02/27 01:46:13]

I will delete this TODO. There is no such concept of Chromium rejecting
drag-and-drop. The function is WebViewImpl::dragTargetDrop. We always accept the
drop except to deal with race condition in IPC.

+                    // not accept the text drop.
+                    mContentViewCore.onPerformDrop(event);
+                    return true;
+                case DragEvent.ACTION_DRAG_EXITED:
+                    mContentViewCore.onDragExited();
+                    return true;
+                case DragEvent.ACTION_DRAG_ENDED:
+                default:
+                    return true;
+            }
         }
 
         @Override