Added a unique command buffer ID for command buffers.

gpu/command_buffer/common/command_buffer.h

Index: gpu/command_buffer/common/command_buffer.h
diff --git a/gpu/command_buffer/common/command_buffer.h b/gpu/command_buffer/common/command_buffer.h
index b69936320eca53013c0110d77743644c97c14834..5fcd30b78f41796f5d8c180e3f3e39438825aaad 100644
--- a/gpu/command_buffer/common/command_buffer.h
+++ b/gpu/command_buffer/common/command_buffer.h
@@ -5,6 +5,7 @@
 #ifndef GPU_COMMAND_BUFFER_COMMON_COMMAND_BUFFER_H_
 #define GPU_COMMAND_BUFFER_COMMON_COMMAND_BUFFER_H_
 
+#include "base/logging.h"
 #include "gpu/command_buffer/common/buffer.h"
 #include "gpu/command_buffer/common/constants.h"
 #include "gpu/gpu_export.h"
@@ -15,6 +16,15 @@ class SharedMemory;
 
 namespace gpu {
 
+enum CommandBufferNamespace {
+  kCommandBufferNamespace_Invalid = -1,
+
+  kCommandBufferNamespace_GpuIO,
+  kCommandBufferNamespace_InProcess,
+
+  NUM_COMMAND_BUFFER_NAMESPACES
+};
+
 // Common interface for CommandBuffer implementations.
 class GPU_EXPORT CommandBuffer {
  public:
@@ -56,7 +66,10 @@ class GPU_EXPORT CommandBuffer {
     std::string message;
   };
 
-  CommandBuffer() {
+  explicit CommandBuffer(CommandBufferNamespace namespace_id,
+                uint64_t command_buffer_id)
+    : namespace_id_(namespace_id),
+      command_buffer_id_(command_buffer_id) {
   }
 
   virtual ~CommandBuffer() {
@@ -126,7 +139,26 @@ class GPU_EXPORT CommandBuffer {
   virtual error::Error GetLastError();
 #endif
 
+  // The namespace and command buffer ID forms a unique pair for all existing
+  // command buffers in a single process. Intermediate command buffers
+  // (such as CommandBufferService) should assign have an invalid namespace
+  // to signify that they should not be queried. Command Buffers that forward
+  // messages to other command buffers should identify as the command buffer
+  // which actually does the executions.
+  CommandBufferNamespace namespace_id() const {
+    DCHECK_NE(namespace_id_, kCommandBufferNamespace_Invalid);
+    return namespace_id_;
+  }
+
+  uint64_t command_buffer_id() const {
+    DCHECK_NE(namespace_id_, kCommandBufferNamespace_Invalid);
+    return command_buffer_id_;
+  }
+
  private:
+  const CommandBufferNamespace namespace_id_;
+  const uint64_t command_buffer_id_;
+
   DISALLOW_COPY_AND_ASSIGN(CommandBuffer);
 };