Set default value of generate_hashtree property to true

Test: presubmit
Test: m
Bug: 190621617
Change-Id: I546730f168632c5d5d41c686853bde93a8ba7911
diff --git a/apex/apex.go b/apex/apex.go
index 33b83c0..7e38b61 100644
--- a/apex/apex.go
+++ b/apex/apex.go
@@ -171,8 +171,7 @@
 	Ignore_system_library_special_case *bool
 
 	// Whenever apex_payload.img of the APEX should include dm-verity hashtree.
-	// Default value is false.
-	// TODO(b/190621617): change default value to true.
+	// Default value is true.
 	Generate_hashtree *bool
 
 	// Whenever apex_payload.img of the APEX should not be dm-verity signed. Should be only
@@ -1320,7 +1319,7 @@
 
 // See the generate_hashtree property
 func (a *apexBundle) shouldGenerateHashtree() bool {
-	return proptools.BoolDefault(a.properties.Generate_hashtree, false)
+	return proptools.BoolDefault(a.properties.Generate_hashtree, true)
 }
 
 // See the test_only_unsigned_payload property