Make WebView respond to device scale change

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 112 matching lines @@
   ScopedJavaLocalRef<jobject> delegate(GetViewAndroidDelegate());
   if (delegate.is_null())
     return;
 
   float scale = display::Screen::GetScreen()
       ->GetDisplayNearestWindow(this)
       .device_scale_factor();
   int left_margin = std::round(bounds.x() * scale);
   // TODO(jinsukkim): Move content_offset() to ViewAndroid, since it's
   //                  specific to a given web contents/render widget.
-  float content_offset_y_pix = GetWindowAndroid()->content_offset().y();
-  int top_margin = std::round(content_offset_y_pix + bounds.y() * scale);
+  int top_margin = std::round(
+      (GetWindowAndroid()->content_offset().y() + bounds.y()) * scale);
   JNIEnv* env = base::android::AttachCurrentThread();
   Java_ViewAndroidDelegate_setViewPosition(env,
                                            delegate.obj(),
                                            anchor.obj(),
                                            bounds.x(),
                                            bounds.y(),
                                            bounds.width(),
                                            bounds.height(),
                                            scale,
                                            left_margin,
@@ skipping 39 matching lines @@
   if (delegate.is_null())
     return;
   JNIEnv* env = base::android::AttachCurrentThread();
   Java_ViewAndroidDelegate_startDragAndDrop(env,
                                             delegate.obj(),
                                             jtext.obj(),
                                             jimage.obj());
 }
 
 }  // namespace ui