Implement flush and finish in RendererGL.

BUG=angleproject:883

Change-Id: Idc474c58d3971c5f7c2c2760cd21aefdf65424b4
Reviewed-on: https://chromium-review.googlesource.com/263502
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/renderer/gl/RendererGL.cpp b/src/libANGLE/renderer/gl/RendererGL.cpp
index 6dde550..89c312f 100644
--- a/src/libANGLE/renderer/gl/RendererGL.cpp
+++ b/src/libANGLE/renderer/gl/RendererGL.cpp
@@ -48,14 +48,14 @@
 
 gl::Error RendererGL::flush()
 {
-    UNIMPLEMENTED();
-    return gl::Error(GL_INVALID_OPERATION);
+    mFunctions->flush();
+    return gl::Error(GL_NO_ERROR);
 }
 
 gl::Error RendererGL::finish()
 {
-    UNIMPLEMENTED();
-    return gl::Error(GL_INVALID_OPERATION);
+    mFunctions->finish();
+    return gl::Error(GL_NO_ERROR);
 }
 
 gl::Error RendererGL::drawArrays(const gl::Data &data, GLenum mode,