EmuGL: Deliver every frame to a callback

To enable multi-touch on a tethered device, allow a callback to be
registered with the OpenGL renderer. On every frame, the framebuffer
is read into system memory and provided to the callback, so it can be
mirrored to the device.

This change is co-dependent on Idae3b026d52ed8dd666cbcdc3f3af80175c90ad3
in external/qemu.

Change-Id: I03c49bc55ed9e66ffb59462333181f77e7e46035

tools/emulator/opengl/host/renderer/main.cpp

@@ -120,7 +120,7 @@ int main(int argc, char *argv[])
     //
     // initialize Framebuffer
     //
-    bool inited = FrameBuffer::initialize(winWidth, winHeight);
+    bool inited = FrameBuffer::initialize(winWidth, winHeight, NULL, NULL);
     if (!inited) {
         fprintf(stderr,"Failed to initialize Framebuffer\n");
         return -1;