Adding check before setting alpha of side pages in a PagedView to prevent constant invalidations.

Change-Id: I4fbb66a851d6cbcd916212e86ed8ba85a9226b02
diff --git a/src/com/android/launcher2/PagedView.java b/src/com/android/launcher2/PagedView.java
index 0e8ffa0..289a48d 100644
--- a/src/com/android/launcher2/PagedView.java
+++ b/src/com/android/launcher2/PagedView.java
@@ -271,7 +271,9 @@
                     dimAlpha = (float) (distanceFromScreenCenter - halfChildWidth) / halfChildWidth;
                     dimAlpha = (dimAlpha * dimAlpha);
                 }
-                layout.setDimmedBitmapAlpha(Math.max(0.0f, Math.min(1.0f, dimAlpha)));
+                dimAlpha = Math.max(0.0f, Math.min(1.0f, dimAlpha));
+                if (Float.compare(dimAlpha, layout.getDimmedBitmapAlpha()) != 0)
+                    layout.setDimmedBitmapAlpha(dimAlpha);
             }
         }
         super.dispatchDraw(canvas);