Revert of current program can be null in ES2/ES3 contexts.

gpu/command_buffer/service/context_state.h

Index: gpu/command_buffer/service/context_state.h
diff --git a/gpu/command_buffer/service/context_state.h b/gpu/command_buffer/service/context_state.h
index 2378eeb3906693caec6f0b98b451a2b5eeedc1c9..6e2d2931883ee8a1f1237e6ff1998a390cfb2be1 100644
--- a/gpu/command_buffer/service/context_state.h
+++ b/gpu/command_buffer/service/context_state.h
@@ -243,27 +243,30 @@
   void SetBoundBuffer(GLenum target, Buffer* buffer);
   void RemoveBoundBuffer(Buffer* buffer);
 
-  void InitGenericAttribs(GLuint max_vertex_attribs) {
-    attrib_values.resize(max_vertex_attribs);
-
-    uint32_t packed_size = max_vertex_attribs / 16;
-    packed_size += (max_vertex_attribs % 16 == 0) ? 0 : 1;
-    generic_attrib_base_type_mask_.resize(packed_size);
-    for (uint32_t i = 0; i < packed_size; ++i) {
-      // All generic attribs are float type by default.
-      generic_attrib_base_type_mask_[i] = 0x55555555u * SHADER_VARIABLE_FLOAT;
-    }
+  void InitGenericAttribBaseType(GLuint 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;
+      generic_attrib_base_type_mask_.resize(packed_size);
+      for (uint32_t i = 0; i < packed_size; ++i) {
+        // All generic attribs are float type by default.
+        generic_attrib_base_type_mask_[i] = 0x55555555u * SHADER_VARIABLE_FLOAT;
+      }
   }
 
   void SetGenericVertexAttribBaseType(GLuint index, GLenum base_type) {
-    DCHECK_LT(index, attrib_values.size());
+    DCHECK(index < max_vertex_attribs_);
     int shift_bits = (index % 16) * 2;
     generic_attrib_base_type_mask_[index / 16] &= ~(0x3 << shift_bits);
     generic_attrib_base_type_mask_[index / 16] |= (base_type << shift_bits);
   }
 
-  const std::vector<uint32_t>& generic_attrib_base_type_mask() const {
-    return generic_attrib_base_type_mask_;
+  // Return 16 attributes' base types, in which the generic attribute
+  // specified by argument 'index' located.
+  uint32_t GetGenericVertexAttribBaseTypeMask(GLuint index) {
+    DCHECK(index < max_vertex_attribs_);
+    return generic_attrib_base_type_mask_[index / 16];
   }
 
   void UnbindTexture(TextureRef* texture);
@@ -343,9 +346,10 @@
 
   bool framebuffer_srgb_;
 
+  uint32_t max_vertex_attribs_;
   // Generic vertex attrib base types: FLOAT, INT, or UINT.
   // Each base type is encoded into 2 bits, the lowest 2 bits for location 0,
-  // the highest 2 bits for location (max_vertex_attribs - 1).
+  // the highest 2 bits for location (max_vertex_attribs_ - 1).
   std::vector<uint32_t> generic_attrib_base_type_mask_;
 
   FeatureInfo* feature_info_;