Revert 236475 "Disable partial swap on Windows."

trunk/src/ui/gl/gl_surface_egl.cc

 // Copyright (c) 2012 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.
 
 // This include must be here so that the includes provided transitively
 // by gl_surface_egl.h don't make it impossible to compile this code.
 #include "third_party/mesa/src/include/GL/osmesa.h"
 
 #include "ui/gl/gl_surface_egl.h"
 
@@ skipping 277 matching lines @@
     return false;
   }
 
   EGLint surfaceVal;
   EGLBoolean retVal = eglQuerySurface(GetDisplay(),
                                       surface_,
                                       EGL_POST_SUB_BUFFER_SUPPORTED_NV,
                                       &surfaceVal);
   supports_post_sub_buffer_ = (surfaceVal && retVal) == EGL_TRUE;
 
-#if defined(OS_WIN)
-  // Partial swaps may be causing performance issues on Windows.
-  supports_post_sub_buffer_ = false;
-#endif
-
   if (sync_provider)
     vsync_provider_.swap(vsync_provider);
   else if (g_egl_sync_control_supported)
     vsync_provider_.reset(new EGLSyncControlVSyncProvider(surface_));
   return true;
 }
 
 void NativeViewGLSurfaceEGL::Destroy() {
   if (surface_) {
     if (!eglDestroySurface(GetDisplay(), surface_)) {
@@ skipping 453 matching lines @@
     }
     default:
       NOTREACHED();
       return NULL;
   }
 }
 
 #endif
 
 }  // namespace gfx