Implement off-screen rendering support using delegated rendering (issue #1257).

This implementation supports both GPU compositing and software compositing (used when GPU is not supported or when passing `--disable-gpu --disable-gpu-compositing` command-line flags). GPU-accelerated features (WebGL and 3D CSS) that did not work with the previous off-screen rendering implementation do work with this implementation when GPU support is available.

Rendering now operates on a per-frame basis. The frame rate is configurable via CefBrowserSettings.windowless_frame_rate up to a maximum of 60fps (potentially limited by how fast the system can generate new frames). CEF generates a bitmap from the compositor backing and passes it to CefRenderHandler::OnPaint.

The previous CefRenderHandler/CefBrowserHost API for off-screen rendering has been restored mostly as-is with some minor changes:

- CefBrowserHost::Invalidate no longer accepts a CefRect region argument. Instead of invalidating a specific region it now triggers generation of a new frame.
- The |dirtyRects| argument to CefRenderHandler::OnPaint will now always be a single CefRect representing the whole view (frame) size. Previously, invalidated regions were listed separately.
- Linux: CefBrowserHost::SendKeyEvent now expects X11 event information instead of GTK event information. See cefclient for an example of converting GTK events to the necessary format.
- Sizes passed to the CefRenderHandler OnPaint and OnPopupSize methods are now already DPI scaled. Previously, the client had to perform DPI scaling.
- Includes drag&drop implementation from issue #1032.
- Includes unit test fixes from issue #1245.

git-svn-id: https://chromiumembedded.googlecode.com/svn/trunk@1751 5089003a-bbd8-11dd-ad1f-f1f9622dbc98

libcef/renderer/browser_impl.h

@@ -75,7 +75,8 @@ class CefBrowserImpl : public CefBrowser,
 
   CefBrowserImpl(content::RenderView* render_view,
                  int browser_id,
-                 bool is_popup);
+                 bool is_popup,
+                 bool is_windowless);
   virtual ~CefBrowserImpl();
 
   void LoadRequest(const CefMsg_LoadRequest_Params& params);
@@ -95,6 +96,7 @@ class CefBrowserImpl : public CefBrowser,
 
   int browser_id() const { return browser_id_; }
   bool is_popup() const { return is_popup_; }
+  bool is_windowless() const { return is_windowless_; }
   content::RenderView* render_view() const {
     return content::RenderViewObserver::render_view();
   }
@@ -137,6 +139,7 @@ class CefBrowserImpl : public CefBrowser,
   // same browser ID.
   int browser_id_;
   bool is_popup_;
+  bool is_windowless_;
 
   // Id of the last frame that had focus.
   int64 last_focused_frame_id_;