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

content/common/input_messages.h

 // Copyright (c) 2013 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.
 
 // IPC messages for input events and other messages that require processing in
 // order relative to input events.
 // Multiply-included message file, hence no include guard.
 
 #include "base/strings/string16.h"
 #include "content/common/content_export.h"
@@ skipping 184 matching lines @@
 IPC_MESSAGE_ROUTED0(InputMsg_SelectAll)
 
 IPC_MESSAGE_ROUTED0(InputMsg_Unselect)
 
 // Requests the renderer to select the region between two points.
 // Expects a SelectRange_ACK message when finished.
 IPC_MESSAGE_ROUTED2(InputMsg_SelectRange,
                     gfx::Point /* start */,
                     gfx::Point /* end */)
 
+// Requests the renderer to move the selection extent point to a new position.
+IPC_MESSAGE_ROUTED1(InputMsg_MoveSelectionExtent,
+                    gfx::Point /* point */)
+
 // Requests the renderer to move the caret selection toward the point.
 // Expects a MoveCaret_ACK message when finished.
 IPC_MESSAGE_ROUTED1(InputMsg_MoveCaret,
                     gfx::Point /* location */)
 
 #if defined(OS_ANDROID)
 // Sent when the user clicks on the find result bar to activate a find result.
 // The point (x,y) is in fractions of the content document's width and height.
 IPC_MESSAGE_ROUTED3(InputMsg_ActivateNearestFindResult,
                     int /* request_id */,
@@ skipping 31 matching lines @@
 // bounds after every composition change to always have correct bound info.
 IPC_MESSAGE_ROUTED2(InputHostMsg_ImeCompositionRangeChanged,
                     gfx::Range /* composition range */,
                     std::vector<gfx::Rect> /* character bounds */)
 #endif
 
 // Adding a new message? Stick to the sort order above: first platform
 // independent InputMsg, then ifdefs for platform specific InputMsg, then
 // platform independent InputHostMsg, then ifdefs for platform specific
 // InputHostMsg.