Ensure VM's heap is accounted correctly.

The meminfo dumping assumes that dalvik heap is created using ashmem and has a
prefix of "dalvik-". Ensure ART's anonymous mmaps fit this pattern. Tidy up
anonymous mmaps so naming is more consistent.

Change-Id: I9c62a9d1da21da6a048effb0399a1f85865cb12d
diff --git a/src/image_writer.cc b/src/image_writer.cc
index dc19d72..e21ff72 100644
--- a/src/image_writer.cc
+++ b/src/image_writer.cc
@@ -143,7 +143,7 @@
 
   int prot = PROT_READ | PROT_WRITE;
   size_t length = RoundUp(size, kPageSize);
-  image_.reset(MemMap::MapAnonymous("image-writer-image", NULL, length, prot));
+  image_.reset(MemMap::MapAnonymous("image writer image", NULL, length, prot));
   if (image_.get() == NULL) {
     LOG(ERROR) << "Failed to allocate memory for image file generation";
     return false;