Fix multisample framebuffer validation ASSERT

Change-Id: I1b02ed7209f30549c17f46aeb3726ba1254df3ea
Reviewed-on: https://chromium-review.googlesource.com/239270
Tested-by: Austin Kinross <aukinros@microsoft.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/validationES.cpp b/src/libANGLE/validationES.cpp
index 80af8a8..9db35c8 100644
--- a/src/libANGLE/validationES.cpp
+++ b/src/libANGLE/validationES.cpp
@@ -339,7 +339,7 @@
 bool ValidateRenderbufferStorageParametersANGLE(gl::Context *context, GLenum target, GLsizei samples,
                                                 GLenum internalformat, GLsizei width, GLsizei height)
 {
-    ASSERT(context->getExtensions().framebufferMultisample);
+    ASSERT(samples == 0 || context->getExtensions().framebufferMultisample);
 
     // ANGLE_framebuffer_multisample states that the value of samples must be less than or equal
     // to MAX_SAMPLES_ANGLE (Context::getExtensions().maxSamples) otherwise GL_INVALID_VALUE is