command_buffer: Fix setting samplers with bound uniforms

gpu/command_buffer/service/program_manager.h

Index: gpu/command_buffer/service/program_manager.h
diff --git a/gpu/command_buffer/service/program_manager.h b/gpu/command_buffer/service/program_manager.h
index a33e32f92d0ebcc7b77f9f4ad2ada1634fc11e44..cf98d0ad943e512c472fc9aabd4866ecdddb4323 100644
--- a/gpu/command_buffer/service/program_manager.h
+++ b/gpu/command_buffer/service/program_manager.h
@@ -255,10 +255,11 @@ class GPU_EXPORT Program : public base::RefCounted<Program> {
   GLint GetFragDataIndex(const std::string& original_name) const;
 
   // Sets the sampler values for a uniform.
-  // This is safe to call for any location. If the location is not
-  // a sampler uniform nothing will happen.
-  // Returns false if fake_location is a sampler and any value
-  // is >= num_texture_units. Returns true otherwise.
+  // This should be called only for valid fake location pointing to
+  // an active uniform.
+  // If the location is not a sampler uniform nothing will happen.
+  // Returns false if fake_location is a sampler and any value is >=
+  // num_texture_units. Returns true otherwise.
   bool SetSamplers(
       GLint num_texture_units, GLint fake_location,
       GLsizei count, const GLint* value);