The problem is that some existing test cases doesn't obey to this rule. For instance, some test cases like gl-vertex-attrib-i-render.html under conformance2/attribs. 

Please feel free to update existing tests if they go against this rule.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c487531682715938285a34298659c53c84cd8ca6

commit c487531682715938285a34298659c53c84cd8ca6
Author: yunchao.he <yunchao.he@intel.com>
Date: Fri Jul 22 16:11:07 2016

WebGL 2: make sure VertexAttrib type match the corresponding attrib type in shader.
Fix bugs in attrib-type-match.html

BUG= 628459 
TEST=conformance2/rendering/attrib-type-match.html
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2148723004
Cr-Commit-Position: refs/heads/master@{#407168}

[modify] https://crrev.com/c487531682715938285a34298659c53c84cd8ca6/gpu/command_buffer/service/context_group.cc
[modify] https://crrev.com/c487531682715938285a34298659c53c84cd8ca6/gpu/command_buffer/service/context_state.cc
[modify] https://crrev.com/c487531682715938285a34298659c53c84cd8ca6/gpu/command_buffer/service/context_state.h
[modify] https://crrev.com/c487531682715938285a34298659c53c84cd8ca6/gpu/command_buffer/service/feature_info.cc
[modify] https://crrev.com/c487531682715938285a34298659c53c84cd8ca6/gpu/command_buffer/service/feature_info.h
[modify] https://crrev.com/c487531682715938285a34298659c53c84cd8ca6/gpu/command_buffer/service/gles2_cmd_decoder.cc
[modify] https://crrev.com/c487531682715938285a34298659c53c84cd8ca6/gpu/command_buffer/service/program_manager.cc
[modify] https://crrev.com/c487531682715938285a34298659c53c84cd8ca6/gpu/command_buffer/service/program_manager.h
[modify] https://crrev.com/c487531682715938285a34298659c53c84cd8ca6/gpu/command_buffer/service/program_manager_unittest.cc
[modify] https://crrev.com/c487531682715938285a34298659c53c84cd8ca6/gpu/command_buffer/service/vertex_attrib_manager.cc
[modify] https://crrev.com/c487531682715938285a34298659c53c84cd8ca6/gpu/command_buffer/service/vertex_attrib_manager.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/cddee2c72b27a928a264263dad86ccc38dc1725b

commit cddee2c72b27a928a264263dad86ccc38dc1725b
Author: yunchao.he <yunchao.he@intel.com>
Date: Fri Jul 22 23:46:05 2016

WebGL 2: Fix nits when check vertexAttrib type with variable type in vertex shader.

See the CL: https://codereview.chromium.org/2148723004

BUG= 628459 
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2175673003
Cr-Commit-Position: refs/heads/master@{#407303}

[modify] https://crrev.com/cddee2c72b27a928a264263dad86ccc38dc1725b/gpu/command_buffer/service/context_state.cc
[modify] https://crrev.com/cddee2c72b27a928a264263dad86ccc38dc1725b/gpu/command_buffer/service/context_state.h
[modify] https://crrev.com/cddee2c72b27a928a264263dad86ccc38dc1725b/gpu/command_buffer/service/feature_info.cc
[modify] https://crrev.com/cddee2c72b27a928a264263dad86ccc38dc1725b/gpu/command_buffer/service/gles2_cmd_decoder.cc
[modify] https://crrev.com/cddee2c72b27a928a264263dad86ccc38dc1725b/gpu/command_buffer/service/vertex_attrib_manager.cc
[modify] https://crrev.com/cddee2c72b27a928a264263dad86ccc38dc1725b/gpu/command_buffer/service/vertex_attrib_manager.h

 Issue 627193  has been merged into this issue.