Introduce XGetImage() for GrabWindowSnapshot() in ChromeOS.

ui/aura/root_window_host_linux.cc

Index: ui/aura/root_window_host_linux.cc
diff --git a/ui/aura/root_window_host_linux.cc b/ui/aura/root_window_host_linux.cc
index d9b9cd38d25b160dc9f1d0fcec3653705cb76afc..5b9952ff4a36803854cbbf64928b051fce112660 100644
--- a/ui/aura/root_window_host_linux.cc
+++ b/ui/aura/root_window_host_linux.cc
@@ -6,6 +6,7 @@
 
 #include <X11/Xatom.h>
 #include <X11/Xcursor/Xcursor.h>
+#include <X11/Xlib.h>
 #include <X11/cursorfont.h>
 #include <X11/extensions/XInput2.h>
 #include <X11/extensions/Xfixes.h>
@@ -29,6 +30,7 @@
 #include "ui/base/view_prop.h"
 #include "ui/base/x/x11_util.h"
 #include "ui/compositor/layer.h"
+#include "ui/gfx/codec/png_codec.h"
 #include "ui/gfx/image/image.h"
 
 using std::max;
@@ -804,6 +806,25 @@ void RootWindowHostLinux::SetFocusWhenShown(bool focus_when_shown) {
   }
 }
 
+bool RootWindowHostLinux::GrabWindowSnapshot(
+    std::vector<unsigned char>* png_representation,
+    const gfx::Rect& snapshot_bounds) {
+  XImage* image = XGetImage(
+      xdisplay_, xwindow_,
+      snapshot_bounds.x(), snapshot_bounds.y(),
+      snapshot_bounds.width(), snapshot_bounds.height(),
+      AllPlanes, ZPixmap);
+
+  unsigned char* data = reinterpret_cast<unsigned char*>(image->data);
+  gfx::PNGCodec::Encode(data, gfx::PNGCodec::FORMAT_BGRA,

[Daniel Erat, 2012/05/14 23:17:40]

I don't love the inflexibility of doing PNG encoding here (and on the UI thread)
instead of handing back raw data.  Are you mostly doing this so you can call
XFree() here without needing to copy the data?

[Jun Mukai, 2012/05/15 22:39:24]

That's why original browser::GrabWindowSnapshot returns PNG format.  Also, the
response format would get unclear if win/mac impls of root_window_host want to
support this method.

+                        snapshot_bounds.size(),
+                        image->width * image->bits_per_pixel / 8,
+                        true, std::vector<gfx::PNGCodec::Comment>(),
+                        png_representation);
+  XFree(image);
+  return true;
+}
+
 void RootWindowHostLinux::PostNativeEvent(
     const base::NativeEvent& native_event) {
   DCHECK(xwindow_);