Updated Renderer::sync to return Error objects.

BUG=angle:520

Change-Id: I8f1f095977bab3848b9215cda1127a71982858b8
Reviewed-on: https://chromium-review.googlesource.com/220800
Reviewed-by: Nicolas Capens <capn@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libGLESv2/Context.cpp b/src/libGLESv2/Context.cpp
index 288564d..eab2dad 100644
--- a/src/libGLESv2/Context.cpp
+++ b/src/libGLESv2/Context.cpp
@@ -1893,9 +1893,9 @@
 }
 
 // Implements glFlush when block is false, glFinish when block is true
-void Context::sync(bool block)
+Error Context::sync(bool block)
 {
-    mRenderer->sync(block);
+    return mRenderer->sync(block);
 }
 
 void Context::recordError(const Error &error)