drm_hwcomposer: Add tracing for the main functions

This will help the profiling efforts, now that all the low-hanging
fruit is gone.

BUG=none
TEST=run systrace, see tracing

Change-Id: I9a149afdea8b84837c19f8e224ce8a7e2db1dd9a
diff --git a/gl_compositor.cpp b/gl_compositor.cpp
index 8d25101..38f1e03 100644
--- a/gl_compositor.cpp
+++ b/gl_compositor.cpp
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#define ATRACE_TAG ATRACE_TAG_GRAPHICS
 #define LOG_TAG "GLCompositor"
 
 #include <sstream>
@@ -35,6 +36,7 @@
 
 #include <ui/GraphicBuffer.h>
 #include <ui/PixelFormat.h>
+#include <utils/Trace.h>
 
 #include <cutils/properties.h>
 #include <sync/sync.h>
@@ -756,6 +758,7 @@
 }
 
 int GLCompositor::DoComposition(const GLComposition &composition) {
+  ATRACE_CALL();
   int ret = 0;
   size_t i;
   std::vector<struct texture_from_handle> layer_textures;