Update touch selection to only modify one selection point at a time.

content/browser/renderer_host/input/touch_selection_controller.cc

 // Copyright 2014 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/renderer_host/input/touch_selection_controller.h"
 
 #include "base/auto_reset.h"
 #include "base/logging.h"
 #include "third_party/WebKit/public/web/WebInputEvent.h"
 
@@ skipping 191 matching lines @@
 
   return false;
 }
 
 void TouchSelectionController::OnHandleDragBegin(const TouchHandle& handle) {
   if (&handle == insertion_handle_.get()) {
     client_->OnSelectionEvent(INSERTION_DRAG_STARTED, handle.position());
     return;
   }
 
+  gfx::PointF base, extent;
   if (&handle == start_selection_handle_.get()) {
-    fixed_handle_position_ =
-        end_selection_handle_->position() + GetEndLineOffset();
+    base = end_selection_handle_->position() + GetEndLineOffset();
+    extent = start_selection_handle_->position() + GetStartLineOffset();
   } else {
-    fixed_handle_position_ =
-        start_selection_handle_->position() + GetStartLineOffset();
+    base = start_selection_handle_->position() + GetStartLineOffset();
+    extent = end_selection_handle_->position() + GetEndLineOffset();
   }
+
+  // When moving the handle we want to move only the extent point. Before doing
+  // so we must make sure that the base point is set correctly.
+  client_->SelectBetweenCoordinates(base, extent);
+
   client_->OnSelectionEvent(SELECTION_DRAG_STARTED, handle.position());
 }
 
 void TouchSelectionController::OnHandleDragUpdate(const TouchHandle& handle,
                                                   const gfx::PointF& position) {
   // As the position corresponds to the bottom left point of the selection
   // bound, offset it by half the corresponding line height.
   gfx::Vector2dF line_offset = &handle == end_selection_handle_.get()
                                    ? GetStartLineOffset()
                                    : GetEndLineOffset();
   gfx::PointF line_position = position + line_offset;
   if (&handle == insertion_handle_.get()) {
     client_->MoveCaret(line_position);
   } else {
-    client_->SelectBetweenCoordinates(fixed_handle_position_, line_position);
+    client_->MoveRangeSelectionExtent(line_position);
   }
 }
 
 void TouchSelectionController::OnHandleDragEnd(const TouchHandle& handle) {
   if (&handle != insertion_handle_.get())
     client_->OnSelectionEvent(SELECTION_DRAG_STOPPED, handle.position());
 }
 
 void TouchSelectionController::OnHandleTapped(const TouchHandle& handle) {
   if (insertion_handle_ && &handle == insertion_handle_.get())
@@ skipping 164 matching lines @@
 }
 
 TouchHandle::AnimationStyle TouchSelectionController::GetAnimationStyle(
     bool was_active) const {
   return was_active && client_->SupportsAnimation()
              ? TouchHandle::ANIMATION_SMOOTH
              : TouchHandle::ANIMATION_NONE;
 }
 
 }  // namespace content