Reduced the complexity of layers composition.

This change also refactors the code base a bit by moving classes out of
OpenGLRenderer into separate headers/implementations. This makes the code
more manageable.

This change also adds documentation for implementation methods. The
undocumented methods are simply Skia's Canvas methods.

Change-Id: I54c68b443580a0129251dddc1a7ac95813d5289e
diff --git a/libs/hwui/Matrix.cpp b/libs/hwui/Matrix.cpp
index e9c7791..877d3bb 100644
--- a/libs/hwui/Matrix.cpp
+++ b/libs/hwui/Matrix.cpp
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-#define LOG_TAG "Matrix"
+#define LOG_TAG "OpenGLRenderer"
 
 #include <math.h>
 #include <stdlib.h>