Simplify projection matrix management.

Store in and use from snapshot, and remove the kFlagOrthoDirty flag,
as it's redundant with kFlagIsFboLayer.

Change-Id: I2bd380192d50117f4ce1fd2058213669a886f406
diff --git a/libs/hwui/Snapshot.h b/libs/hwui/Snapshot.h
index 038aea8..aede079 100644
--- a/libs/hwui/Snapshot.h
+++ b/libs/hwui/Snapshot.h
@@ -65,17 +65,16 @@
          * Indicates that this snapshot is a special type of layer
          * backed by an FBO. This flag only makes sense when the
          * flag kFlagIsLayer is also set.
+         *
+         * Viewport has been modified to fit the new Fbo, and must be
+         * restored when this snapshot is restored.
          */
         kFlagIsFboLayer = 0x4,
         /**
-         * Indicates that this snapshot has changed the ortho matrix.
-         */
-        kFlagDirtyOrtho = 0x8,
-        /**
          * Indicates that this snapshot or an ancestor snapshot is
          * an FBO layer.
          */
-        kFlagFboTarget = 0x10
+        kFlagFboTarget = 0x8,
     };
 
     /**
@@ -183,7 +182,7 @@
     int height;
 
     /**
-     * Contains the previous ortho matrix.
+     * Contains the current orthographic, projection matrix.
      */
     mat4 orthoMatrix;