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

patch/patches/webkit_popups.patch

@@ -0,0 +1,76 @@
+Index: public/web/WebView.h
+===================================================================
+--- public/web/WebView.h	(revision 175829)
++++ public/web/WebView.h	(working copy)
+@@ -416,6 +416,7 @@
+ 
+     // Sets whether select popup menus should be rendered by the browser.
+     BLINK_EXPORT static void setUseExternalPopupMenus(bool);
++    virtual void setUseExternalPopupMenusThisInstance(bool) = 0;
+ 
+     // Hides any popup (suggestions, selects...) that might be showing.
+     virtual void hidePopups() = 0;
+Index: Source/web/ChromeClientImpl.cpp
+===================================================================
+--- Source/web/ChromeClientImpl.cpp	(revision 175829)
++++ Source/web/ChromeClientImpl.cpp	(working copy)
+@@ -729,7 +729,7 @@
+ 
+ PassRefPtr<PopupMenu> ChromeClientImpl::createPopupMenu(LocalFrame& frame, PopupMenuClient* client) const
+ {
+-    if (WebViewImpl::useExternalPopupMenus())
++    if (m_webView->useExternalPopupMenus())
+         return adoptRef(new ExternalPopupMenu(frame, client, *m_webView));
+ 
+     return adoptRef(new PopupMenuChromium(frame, client));
+Index: Source/web/WebViewImpl.cpp
+===================================================================
+--- Source/web/WebViewImpl.cpp	(revision 175829)
++++ Source/web/WebViewImpl.cpp	(working copy)
+@@ -365,6 +365,7 @@
+     , m_fakePageScaleAnimationPageScaleFactor(0)
+     , m_fakePageScaleAnimationUseAnchor(false)
+     , m_contextMenuAllowed(false)
++    , m_shouldUseExternalPopupMenus(shouldUseExternalPopupMenus)
+     , m_doingDragAndDrop(false)
+     , m_ignoreInputEvents(false)
+     , m_compositorDeviceScaleFactorOverride(0)
+@@ -3628,9 +3629,14 @@
+     updateLayerTreeViewport();
+ }
+ 
++void WebViewImpl::setUseExternalPopupMenusThisInstance(bool useExternalPopupMenus)
++{
++    m_shouldUseExternalPopupMenus = useExternalPopupMenus;
++}
++
+ bool WebViewImpl::useExternalPopupMenus()
+ {
+-    return shouldUseExternalPopupMenus;
++    return m_shouldUseExternalPopupMenus;
+ }
+ 
+ void WebViewImpl::startDragging(LocalFrame* frame,
+Index: Source/web/WebViewImpl.h
+===================================================================
+--- Source/web/WebViewImpl.h	(revision 175829)
++++ Source/web/WebViewImpl.h	(working copy)
+@@ -352,7 +352,8 @@
+ 
+     // Returns true if popup menus should be rendered by the browser, false if
+     // they should be rendered by WebKit (which is the default).
+-    static bool useExternalPopupMenus();
++    void setUseExternalPopupMenusThisInstance(bool);
++    bool useExternalPopupMenus();
+ 
+     bool contextMenuAllowed() const
+     {
+@@ -628,6 +629,8 @@
+ 
+     bool m_contextMenuAllowed;
+ 
++    bool m_shouldUseExternalPopupMenus;
++
+     bool m_doingDragAndDrop;
+ 
+     bool m_ignoreInputEvents;