Support GL_ANGLE_texture_multisample extension. This patch adds enums of multisampled texture and texStorage2DMultisampleANGLE API. TEST=angle_end2end_tests.exe --gtest_filter=TextureMultisampleTest* TEST=angle_end2end_tests.exe --gtest_filter=NegativeTextureMultisampleTest.Negtive* BUG=angleproject:2275 Change-Id: I2cab997edc33aa2d0be6082381545335423f64e0 Reviewed-on: https://chromium-review.googlesource.com/c/804613 Commit-Queue: Yizhou Jiang <yizhou.jiang@intel.com> Reviewed-by: Geoff Lang <geofflang@chromium.org>
