current program can be null in ES2/ES3 contexts.

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 2e18356ccae22edcaac6af37b76778a843901a03..b344a7726ee431f7f50bd9dacadb6c3fc8a0cdf5 100644
--- a/gpu/command_buffer/service/vertex_attrib_manager.cc
+++ b/gpu/command_buffer/service/vertex_attrib_manager.cc
@@ -127,9 +127,8 @@ VertexAttribManager::~VertexAttribManager() {
 void VertexAttribManager::Initialize(uint32_t max_vertex_attribs,
                                      bool init_attribs) {
   vertex_attribs_.resize(max_vertex_attribs);
-  max_vertex_attribs_ = max_vertex_attribs;
-  uint32_t packed_size = max_vertex_attribs_ / 16;
-  packed_size += (max_vertex_attribs_ % 16 == 0) ? 0 : 1;
+  uint32_t packed_size = max_vertex_attribs / 16;
+  packed_size += (max_vertex_attribs % 16 == 0) ? 0 : 1;

[piman, 2016/07/25 20:04:04]

nit: ditto, uint32_t packed_size = (max_vertex_attribs + 15) / 16;

   attrib_base_type_mask_.resize(packed_size);
   attrib_enabled_mask_.resize(packed_size);
 
@@ -157,18 +156,16 @@ bool VertexAttribManager::Enable(GLuint index, bool enable) {
     return false;
   }
 
-  DCHECK(index < max_vertex_attribs_);
-  GLuint shift_bits = (index % 16) * 2;
-  if (enable) {
-    attrib_enabled_mask_[index / 16] |= (0x3 << shift_bits);
-  } else {
-    attrib_enabled_mask_[index / 16] &= ~(0x3 << shift_bits);
-  }
-
   VertexAttrib& info = vertex_attribs_[index];
   if (info.enabled() != enable) {
     info.set_enabled(enable);
     info.SetList(enable ? &enabled_vertex_attribs_ : &disabled_vertex_attribs_);
+    GLuint shift_bits = (index % 16) * 2;

[Zhenyao Mo, 2016/07/23 16:10:40]

We only need to do this if the glEnableDisable call actually change the state. 
This is to fit with the rest of the code - less confusing.

[yunchao, 2016/07/24 04:52:13]

Acknowledged.

+    if (enable) {
+      attrib_enabled_mask_[index / 16] |= (0x3 << shift_bits);
+    } else {
+      attrib_enabled_mask_[index / 16] &= ~(0x3 << shift_bits);
+    }
   }
   return true;
 }