Improve dumping of display list memory usage

The first step of improving is measuring. So measure better.

Bug: 138856108
Test: dump
Change-Id: I076b904a1f0dfb209622c76bcb8778a10cd2b7db
diff --git a/libs/hwui/utils/LinearAllocator.h b/libs/hwui/utils/LinearAllocator.h
index 9c4a1be..539e654 100644
--- a/libs/hwui/utils/LinearAllocator.h
+++ b/libs/hwui/utils/LinearAllocator.h
@@ -115,6 +115,7 @@
      * wasted)
      */
     size_t usedSize() const { return mTotalAllocated - mWastedSpace; }
+    size_t allocatedSize() const { return mTotalAllocated; }
 
 private:
     LinearAllocator(const LinearAllocator& other);