Make valgrind happier and stop us leaking so much we can can't run the tests on a device.

Change-Id: Id8f45dde788fd84c10b0b5807b2d12eae529ba5e
diff --git a/src/assembler.cc b/src/assembler.cc
index 193d73f..9e67f12 100644
--- a/src/assembler.cc
+++ b/src/assembler.cc
@@ -67,6 +67,7 @@
 
 
 AssemblerBuffer::~AssemblerBuffer() {
+  delete[] contents_;
 }