Add ES3 commands GetVertexAttribI{u}iv to GPU command buffer.

gpu/command_buffer/service/vertex_attrib_manager.cc

Index: gpu/command_buffer/service/vertex_attrib_manager.cc
diff --git a/gpu/command_buffer/service/vertex_attrib_manager.cc b/gpu/command_buffer/service/vertex_attrib_manager.cc
index 8725c4f9533c5ce75b5205f92a7ef404184dd8b4..b7ead54f6dcb06c39f296ad0905163a0fd17c17d 100644
--- a/gpu/command_buffer/service/vertex_attrib_manager.cc
+++ b/gpu/command_buffer/service/vertex_attrib_manager.cc
@@ -35,6 +35,7 @@ VertexAttrib::VertexAttrib()
       gl_stride_(0),
       real_stride_(16),
       divisor_(0),
+      integer_(GL_FALSE),

[Zhenyao Mo, 2015/05/08 22:20:56]

We don't have a path to set this to true in this CL.  I decided to do it in a
followup CL because that requires interaction with a bunch of other commands'
handling.

       is_client_side_array_(false),
       list_(NULL) {
 }