Mac: Add partial swap support to NSOpenGLContext path

ui/accelerated_widget_mac/io_surface_ns_gl_surface.mm

 // Copyright 2015 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/accelerated_widget_mac/io_surface_ns_gl_surface.h"
 
 #include <OpenGL/GL.h>
 
 #include "base/callback_helpers.h"
 #include "base/mac/bind_objc_block.h"
@@ skipping 47 matching lines @@
 
 IOSurfaceNSGLSurface::~IOSurfaceNSGLSurface() {
   [ns_gl_context_ makeCurrentContext];
   iosurface_ = NULL;
   [NSOpenGLContext clearCurrentContext];
   [ns_gl_context_ clearDrawable];
 }
 
 bool IOSurfaceNSGLSurface::GotFrame(IOSurfaceID io_surface_id,
                                     gfx::Size frame_pixel_size,
-                                    float frame_scale_factor) {
+                                    float frame_scale_factor,
+                                    gfx::Rect pixel_damage_rect) {
   // The OpenGL framebuffer's scale factor and pixel size are updated to match
   // the CALayer's contentsScale and bounds at setView. The pixel size is the
   // stored in the GL_VIEWPORT state of the context.
   gfx::Size contents_pixel_size;
   float contents_scale_factor = [[view_ layer] contentsScale];
   {
     [ns_gl_context_ makeCurrentContext];
     GLint viewport[4];
     glGetIntegerv(GL_VIEWPORT, viewport);
     [NSOpenGLContext clearCurrentContext];
     contents_pixel_size = gfx::Size(viewport[2], viewport[3]);
   }
 
   // If the OpenGL framebuffer does not match the frame in scale factor or
   // pixel size, then re-latch them. Note that they will latch to the layer's
   // bounds, which will not necessarily match the frame's pixel size.
+  bool full_damage = false;
   if (frame_pixel_size != contents_pixel_size ||
       frame_scale_factor != contents_scale_factor) {
     ScopedCAActionDisabler disabler;
     [ns_gl_context_ clearDrawable];
     [[view_ layer] setContentsScale:frame_scale_factor];
     [ns_gl_context_ setView:view_];
+
+    // The front buffer may have been destroyed at re-creation, so re-draw
+    // everything.
+    full_damage = true;
   }
 
   bool result = true;
   [ns_gl_context_ makeCurrentContext];
   result &= iosurface_->SetIOSurface(io_surface_id, frame_pixel_size);
-  result &= iosurface_->DrawIOSurface();
+  if (full_damage)
+    result &= iosurface_->DrawIOSurface();
+  else
+    result &= iosurface_->DrawIOSurfaceWithDamageRect(pixel_damage_rect);
   glFlush();
   [NSOpenGLContext clearCurrentContext];
   return result;
 }
 
 };