(not for review) Fix composited-to-non-composited corruption on Linux.

ui/gl/gl_surface_glx.cc

Index: ui/gl/gl_surface_glx.cc
diff --git a/ui/gl/gl_surface_glx.cc b/ui/gl/gl_surface_glx.cc
index 02e5a2a3d1cd257ad735be08549198d234290b2e..2dba6d38ca4956233a98a35404cebb0dfab2f1ea 100644
--- a/ui/gl/gl_surface_glx.cc
+++ b/ui/gl/gl_surface_glx.cc
@@ -311,6 +311,7 @@ class XExposeEventForwarder : public base::MessagePumpObserver {
   XExposeEventForwarder() {}
   virtual ~XExposeEventForwarder() {
     DCHECK(child_to_parent_map_.empty());
+    DCHECK(parent_to_child_map_.empty());
   }
   void AddParentChildPair(gfx::AcceleratedWidget parent_window,
                           gfx::AcceleratedWidget child_window) {
@@ -321,16 +322,33 @@ class XExposeEventForwarder : public base::MessagePumpObserver {
            child_to_parent_map_.end());
     child_to_parent_map_.insert(std::make_pair(
         child_window, parent_window));
+    parent_to_child_map_.insert(std::make_pair(
+        parent_window, child_window));
   }
   void RemoveParentChildPair(gfx::AcceleratedWidget parent_window,
                              gfx::AcceleratedWidget child_window) {
     DCHECK(child_to_parent_map_.find(child_window) !=
            child_to_parent_map_.end());
+    DCHECK(parent_to_child_map_.find(parent_window) !=
+           parent_to_child_map_.end());
     child_to_parent_map_.erase(child_window);
+    parent_to_child_map_.erase(parent_window);
 
     if (child_to_parent_map_.empty())
       base::MessagePumpX11::Current()->RemoveObserver(this);
   }
+  void SetChildWindowVisible(gfx::AcceleratedWidget parent_window,
+                             bool visible) {
+    WindowMap::const_iterator found = parent_to_child_map_.find(parent_window);
+    if (found == parent_to_child_map_.end())
+      return;
+    gfx::AcceleratedWidget child_window = found->second;
+    if (visible)
+      XMapWindow(g_display, child_window);
+    else
+      XUnmapWindow(g_display, child_window);
+    // XFlush(g_display);
+  }
 
  private:
   virtual base::EventStatus WillProcessEvent (
@@ -355,6 +373,7 @@ class XExposeEventForwarder : public base::MessagePumpObserver {
 
   typedef std::map<gfx::AcceleratedWidget, gfx::AcceleratedWidget> WindowMap;
   WindowMap child_to_parent_map_;
+  WindowMap parent_to_child_map_;
 
   DISALLOW_COPY_AND_ASSIGN(XExposeEventForwarder);
 };
@@ -390,10 +409,6 @@ bool GLSurfaceGLX::InitializeOneOff() {
       base::MessageLoop::current() &&
       base::MessageLoop::current()->type() == base::MessageLoop::TYPE_GPU;
 
-  // Disable this path because it is causing window contents to disappear.
-  // http://crbug.com/292655
-  g_create_child_windows = false;
-
   if (g_create_child_windows)
     g_display = base::MessagePumpX11::GetDefaultXDisplay();
   else
@@ -697,6 +712,14 @@ VSyncProvider* NativeViewGLSurfaceGLX::GetVSyncProvider() {
   return vsync_provider_.get();
 }
 
+#if defined(TOOLKIT_GTK)
+void NativeViewGLSurfaceGLX::AcceleratedCompositingStateChange(
+    int32 surface_id, bool compositing_active) {
+  g_xexpose_event_forwarder.Pointer()->SetChildWindowVisible(
+      surface_id, compositing_active);
+}
+#endif
+
 NativeViewGLSurfaceGLX::NativeViewGLSurfaceGLX()
   : parent_window_(0),
 #if defined(TOOLKIT_GTK)