Lazily allocate the mBounds Rect in Drawable.

For background, see:
http://kohlerm.blogspot.com/2009/04/analyzing-memory-usage-off-your-android.html

Thanks, Markus!

graphics/java/android/graphics/drawable/Drawable.java

@@ -101,7 +101,7 @@ public abstract class Drawable {
     private int[] mStateSet = StateSet.WILD_CARD;
     private int mLevel = 0;
     private int mChangingConfigurations = 0;
-    private Rect mBounds = ZERO_BOUNDS_RECT;
+    private Rect mBounds = ZERO_BOUNDS_RECT;  // lazily becomes a new Rect()
     /*package*/ Callback mCallback = null;
     private boolean mVisible = true;