Fix the computation of the size of the stack maps region.

In art::StackMapStream::ComputeStackMapSize, compute the
size of a CodeInfo's stack maps region using the stack
mask size, not the maximum element of the stack mask.
Also, rename this method as
art::StackMapStream::ComputeStackMapsSize to make it clear
it that it covers all the stack maps of the CodeInfo item,
not just one stack map.

Change-Id: Icad21946dbca6e1ade2b82c9c2c535fdfed110a9
diff --git a/runtime/stack_map.h b/runtime/stack_map.h
index e88820f..3856da3 100644
--- a/runtime/stack_map.h
+++ b/runtime/stack_map.h
@@ -606,10 +606,17 @@
     region_.Store<uint32_t>(kNumberOfStackMapsOffset, number_of_stack_maps);
   }
 
+  // Get the size of one stack map of this CodeInfo object, in bytes.
+  // All stack maps of a CodeInfo have the same size.
   size_t StackMapSize() const {
     return StackMap::ComputeAlignedStackMapSize(GetStackMaskSize());
   }
 
+  // Get the size all the stack maps of this CodeInfo object, in bytes.
+  size_t StackMapsSize() const {
+    return StackMapSize() * GetNumberOfStackMaps();
+  }
+
   uint32_t GetStackMapsOffset() const {
     return kFixedSize;
   }
@@ -663,7 +670,7 @@
   MemoryRegion GetStackMaps() const {
     return region_.size() == 0
         ? MemoryRegion()
-        : region_.Subregion(kFixedSize, StackMapSize() * GetNumberOfStackMaps());
+        : region_.Subregion(kFixedSize, StackMapsSize());
   }
 
   // Compute the size of a Dex register map starting at offset `origin` in