Initialize RenderWidget's compositing_surface_ to kNullPluginWindow. This...

Initialize RenderWidget's compositing_surface_ to kNullPluginWindow. This avoids passing garbage down to the GL layers in the test case attached to the bug below. 
Note that this does not fix the bug, but will avoid potential memory corruption and suppress spurious window system errors. 

BUG=80703
TEST=run the "canvas-popup.html" test case in the bug. check the chrome_debug.log to see that no EGL or X errors are present.
Review URL: http://codereview.chromium.org/7134049

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@88563 0039d316-1c4b-4281-b951-d872f2087c98

content/renderer/render_widget.cc

@@ -88,6 +88,7 @@ RenderWidget::RenderWidget(RenderThreadBase* render_thread,
       pending_window_rect_count_(0),
       suppress_next_char_events_(false),
       is_accelerated_compositing_active_(false),
+      compositing_surface_(gfx::kNullPluginWindow),
       animation_update_pending_(false),
       animation_task_posted_(false),
       invalidation_task_posted_(false) {