Subzero: Use C++11 member initializers where practical.

Also change the pattern "foo() {}" into "foo() = default;" for ctors and dtors.

Generally avoids initializing unique_ptr<> members to nullptr in a .h file, because that requires knowing the definition of the underlying class which may not be available to all includers.

BUG= none
R=jpp@chromium.org

Review URL: https://codereview.chromium.org/1197223002
diff --git a/src/IceAssembler.cpp b/src/IceAssembler.cpp
index a0500d6..e160612 100644
--- a/src/IceAssembler.cpp
+++ b/src/IceAssembler.cpp
@@ -88,7 +88,7 @@
   assert(size() == 0);
 }
 
-AssemblerBuffer::~AssemblerBuffer() {}
+AssemblerBuffer::~AssemblerBuffer() = default;
 
 void AssemblerBuffer::extendCapacity() {
   intptr_t old_size = size();