GraphicsContextGLANGLE does not validate clearBuffers value length
<rdar://125222153>
Pull request: https://github.com/WebKit/WebKit/pull/26401
Pull request: https://github.com/apple/WebKit/pull/1155
Committed 272448.803@safari-7618-branch (89ee93bd2ea4): <https://commits.webkit.org/272448.803@safari-7618-branch> Reviewed commits have been landed. Closing PR #1155 and removing active labels.