Label the libwebview address space reservation.

So it shows up in showmaps output as "[anon:libwebview reservation]"
instead of grouped in with the rest of "[anon]", to facilitate memory
debugging.

Test: Manually confirm libwebview reservation shows up in system server showmap.
Change-Id: I4897aff4406265a7be9fc37aecbe5967bcf29426
diff --git a/native/webview/loader/loader.cpp b/native/webview/loader/loader.cpp
index adb371d..d0b4754 100644
--- a/native/webview/loader/loader.cpp
+++ b/native/webview/loader/loader.cpp
@@ -26,6 +26,7 @@
 #include <string.h>
 #include <unistd.h>
 #include <sys/mman.h>
+#include <sys/prctl.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 
@@ -58,6 +59,7 @@
           vsize, strerror(errno));
     return JNI_FALSE;
   }
+  prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, addr, vsize, "libwebview reservation");
   gReservedAddress = addr;
   gReservedSize = vsize;
   ALOGV("Reserved %zd bytes at %p", vsize, addr);