Add region-tracking to OffscreenBuffers

Change-Id: I024c7219c080b9a89888517f5a89d49dfe8065ba
diff --git a/libs/hwui/utils/FatVector.h b/libs/hwui/utils/FatVector.h
index c3c16c5a..315c249 100644
--- a/libs/hwui/utils/FatVector.h
+++ b/libs/hwui/utils/FatVector.h
@@ -91,6 +91,10 @@
             InlineStdAllocator<T, SIZE>(mAllocation)) {
         this->reserve(SIZE);
     }
+
+    FatVector(size_t capacity) : FatVector() {
+        this->resize(capacity);
+    }
 private:
     typename InlineStdAllocator<T, SIZE>::Allocation mAllocation;
 };