gpu/ texture_upload_perftest.cc: better CheckNoGlError()

This CL teaches CheckNoGlError() in texture_upload_perftest.cc to
dump the GL error as human readable string.

Bug: 920626
Change-Id: I49c9ad3db9f343f0a031a7bce8505f99c6e4b832
Reviewed-on: https://chromium-review.googlesource.com/c/1440521
Commit-Queue: Miguel Casas <mcasas@chromium.org>
Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Auto-Submit: Miguel Casas <mcasas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#627040}

gpu/perftests/texture_upload_perftest.cc

@@ -64,7 +64,9 @@ SHADER(
 // clang-format on
 
 void CheckNoGlError(const std::string& msg) {
-  CHECK_EQ(static_cast<GLenum>(GL_NO_ERROR), glGetError()) << " " << msg;
+  const GLenum error = glGetError();
+  CHECK_EQ(static_cast<GLenum>(GL_NO_ERROR), error)
+      << msg << " " << gl::GLEnums::GetStringError(error);
 }
 
 // Utility function to compile a shader from a string.