Rename CommandWriter to CommandWriterBase

CommandWriter will be used as a base class in extensions of HWC. Renamed
for consistency.

Bug: 33297385
Test: Compiled
Change-Id: Iabe59f37157062961b916d55108cb9f4fb792619
diff --git a/graphics/composer/2.1/default/HwcClient.h b/graphics/composer/2.1/default/HwcClient.h
index c719774..35a0450 100644
--- a/graphics/composer/2.1/default/HwcClient.h
+++ b/graphics/composer/2.1/default/HwcClient.h
@@ -171,7 +171,7 @@
 
         HwcClient& mClient;
         HwcHal& mHal;
-        CommandWriter& mWriter;
+        CommandWriterBase& mWriter;
 
         Display mDisplay;
         Layer mLayer;
@@ -184,7 +184,7 @@
         64 * 1024 / sizeof(uint32_t) - 16;
     std::mutex mCommandMutex;
     CommandReader mReader;
-    CommandWriter mWriter;
+    CommandWriterBase mWriter;
 
     sp<IComposerCallback> mCallback;