ANGLETest: set viewport after resizing to help apitrace

Otherwise apitrace doesn't know the dimension of the framebuffer and
cannot display it.

BUG=angleproject:892

Change-Id: Ib8ad846ca80e4783ab77c96430bb5220df1a39ab
Reviewed-on: https://chromium-review.googlesource.com/286881
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/tests/test_utils/ANGLETest.cpp b/src/tests/test_utils/ANGLETest.cpp
index dad58f0..7aa6c8c 100644
--- a/src/tests/test_utils/ANGLETest.cpp
+++ b/src/tests/test_utils/ANGLETest.cpp
@@ -29,6 +29,11 @@
     // which will allow follow-up test code to assume the framebuffer covers
     // the whole window.
     swapBuffers();
+
+    // This Viewport command is not strictly necessary but we add it so that programs
+    // taking OpenGL traces can guess the size of the default framebuffer and show it
+    // in their UIs
+    glViewport(0, 0, mEGLWindow->getWidth(), mEGLWindow->getHeight());
 }
 
 void ANGLETest::TearDown()