Drop the backbuffer on hidden tabs on GLX image transport.

content/common/gpu/image_transport_surface_linux.cc

Index: content/common/gpu/image_transport_surface_linux.cc
diff --git a/content/common/gpu/image_transport_surface_linux.cc b/content/common/gpu/image_transport_surface_linux.cc
index a394c9b6a7b8fe6449ee3c35f5e96500bd2e8fff..5cc75badd1c9ad9060a167ee30257e2448479014 100644
--- a/content/common/gpu/image_transport_surface_linux.cc
+++ b/content/common/gpu/image_transport_surface_linux.cc
@@ -112,6 +112,7 @@ class GLXImageTransportSurface : public ImageTransportSurface,
   virtual bool SwapBuffers() OVERRIDE;
   virtual gfx::Size GetSize() OVERRIDE;
   virtual bool OnMakeCurrent(gfx::GLContext* context) OVERRIDE;
+  virtual void SetVisible(bool visible) OVERRIDE;
 
  protected:
   // ImageTransportSurface implementation:
@@ -461,6 +462,17 @@ void GLXImageTransportSurface::ReleaseSurface() {
   bound_ = false;
 }
 
+void GLXImageTransportSurface::SetVisible(bool visible) {
+  Display* dpy = static_cast<Display*>(GetDisplay());
+  if (!visible) {
+    XResizeWindow(dpy, window_, 1, 1);
+  } else {
+    XResizeWindow(dpy, window_, size_.width(), size_.height());
+    needs_resize_ = true;
+  }
+  glXWaitX();
+}
+
 void GLXImageTransportSurface::OnResize(gfx::Size size) {
   TRACE_EVENT0("gpu", "GLXImageTransportSurface::OnResize");
   size_ = size;