emulator opengl: guest/host rendering syncronization.

Added a return value for rcFlushWindowColorBuffer and
rcUpdateColorBuffer in order to make those calls to block
with a round-trip to the host. This is to make sure that
the color buffer is up-to-date before the flinger use it
for rendering.
Also added a call to the native windows's lock function after
EGL is attached and bound to render on the window. This call
was missed before.

This syncronization can be optimized by removing the round-trip
and insert sync primitive to the stream at every draw command that
reads from a color buffer to make the sync happen on the host
before rendering the color buffer and remove the need for the
guest to wait for that update.

Change-Id: I1c2d8bc407b69663e992a68d5aa755f19bbe0ec3

tools/emulator/opengl/system/egl/egl.cpp

@@ -325,8 +325,12 @@ EGLBoolean egl_window_surface_t::connect()
     if (nativeWindow->dequeueBuffer(nativeWindow, &buffer) != NO_ERROR) {
         setErrorReturn(EGL_BAD_ALLOC, EGL_FALSE);
     }
+
     buffer->common.incRef(&buffer->common);
 
+    // lock the buffer
+    nativeWindow->lockBuffer(nativeWindow, buffer);
+
     DEFINE_AND_VALIDATE_HOST_CONNECTION(EGL_FALSE);
     rcEnc->rcSetWindowColorBuffer(rcEnc, rcSurface, ((cb_handle_t *)(buffer->handle))->hostHandle);
 
@@ -360,6 +364,9 @@ EGLBoolean egl_window_surface_t::swapBuffers()
         setErrorReturn(EGL_BAD_ALLOC, EGL_FALSE);
     }
 
+    // lock the buffer
+    nativeWindow->lockBuffer(nativeWindow, buffer);
+
     rcEnc->rcSetWindowColorBuffer(rcEnc, rcSurface, ((cb_handle_t *)(buffer->handle))->hostHandle);
 
     return EGL_TRUE;