Update maxIntegerSamples, maxDepthTextureSamples and maxColorTextureSamples
if the extension is enabled on ES 3.0.

TEST=TextureMultisampleTest.*
TEST=NegativeTextureMultisampleTest.Negtive*

BUG=angleproject:2275

Change-Id: I8c215f990ff5d93611b1bc89de9a43f3d392e8d4
Reviewed-on: https://chromium-review.googlesource.com/c/1319251Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jiajia Qin <jiajia.qin@intel.com>
Commit-Queue: Yizhou Jiang <yizhou.jiang@intel.com>