Fix the scale of Drag and Drop shadow image.

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/android/jni_android.h"
 #include "base/android/jni_string.h"
 #include "base/logging.h"
 #include "content/browser/android/content_view_core_impl.h"
@@ skipping 231 matching lines @@
   if (!native_view) {
     // Need to clear drag and drop state in blink.
     OnDragEnded();
     return;
   }
 
   JNIEnv* env = AttachCurrentThread();
   ScopedJavaLocalRef<jstring> jtext =
       ConvertUTF16ToJavaString(env, drop_data.text.string());
 
+  float page_scale = content_view_core_->page_scale();
+  // No way to scale image.bitmap() itself. So we need to pass the page scale
+  // here and let the embedder do the scaling.
   if (!native_view->StartDragAndDrop(
-          jtext, gfx::ConvertToJavaBitmap(image.bitmap()))) {
+          jtext, gfx::ConvertToJavaBitmap(image.bitmap()), page_scale)) {

[Ted C, 2016/09/20 20:05:24]

who generates the bitmap?

In this case, were we generating it to be too large?  If so, we should really
try to fix it at generation time to be scaled down to avoid passing a bigger
bitmap across to java (since it will use more memory for something we don't
actually need).

[hush (inactive), 2016/09/20 21:32:33]

Blink generates it here.
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/page/Drag...

It is not always bigger than what's needed though:
if page scale is < 1, the bitmap is bigger than necessary. Otherwise, it is
smaller than necessary.

     // Need to clear drag and drop state in blink.
     OnDragEnded();
     return;
   }
 
   if (content_view_core_)
     content_view_core_->HidePopupsAndPreserveSelection();
 }
 
 void WebContentsViewAndroid::UpdateDragCursor(blink::WebDragOperation op) {
@@ skipping 44 matching lines @@
 // 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