[CRD iOS] Preserve viewport state when toggling the soft keyboard

remoting/client/ui/desktop_viewport.cc

 // Copyright 2017 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 "remoting/client/ui/desktop_viewport.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 
@@ skipping 17 matching lines @@
   desktop_size_.x = desktop_width;
   desktop_size_.y = desktop_height;
   ResizeToFit();
 }
 
 void DesktopViewport::SetSurfaceSize(int surface_width, int surface_height) {
   if (surface_width == surface_size_.x && surface_height == surface_size_.y) {
     return;
   }
 
+  // Only reset the viewport if both dimensions have changed, otherwise keep
+  // the offset and scale and just change the constraint. This is to cover these
+  // use cases:
+  // * Rotation => Reset
+  // * Keyboard => No reset
+  // * Settings menu => No reset
+  //
+  // TODO(yuweih): This is probably too much inferring. Let the caller to decide
+  // when to call ResizeToFit() if things don't work right.
+  bool need_to_reset =
+      surface_width != surface_size_.x && surface_height != surface_size_.y;
+
   surface_size_.x = surface_width;
   surface_size_.y = surface_height;
-  ResizeToFit();
+
+  if (need_to_reset) {
+    ResizeToFit();
+    return;
+  }
+
+  UpdateViewport();
 }
 
 void DesktopViewport::MoveDesktop(float dx, float dy) {
   desktop_to_surface_transform_.PostTranslate({dx, dy});
   UpdateViewport();
 }
 
 void DesktopViewport::ScaleDesktop(float px, float py, float scale) {
   desktop_to_surface_transform_.PostScale({px, py}, scale);
   UpdateViewport();
@@ skipping 211 matching lines @@
 
   if (new_point.y < bounds.top) {
     new_point.y = bounds.top;
   } else if (new_point.y > bounds.bottom) {
     new_point.y = bounds.bottom;
   }
   return new_point;
 }
 
 }  // namespace remoting