Add a default constructor for VarArrayBuffer, so that it can be used by ext::DictField.

ppapi/cpp/var_array_buffer.cc

Index: ppapi/cpp/var_array_buffer.cc
diff --git a/ppapi/cpp/var_array_buffer.cc b/ppapi/cpp/var_array_buffer.cc
index c05a8eb81898a145e1873590365d9e0f08303fd4..0bc8ea57ad779c8d51f2d44d63e80d9ec27aef02 100644
--- a/ppapi/cpp/var_array_buffer.cc
+++ b/ppapi/cpp/var_array_buffer.cc
@@ -20,6 +20,10 @@ template <> const char* interface_name<PPB_VarArrayBuffer_1_0>() {
 
 }  // namespace
 
+VarArrayBuffer::VarArrayBuffer() {
+  ConstructWithSize(0);
+}
+
 VarArrayBuffer::VarArrayBuffer(const Var& var) : Var(var) {
   if (!var.is_array_buffer()) {
     PP_NOTREACHED();
@@ -28,13 +32,7 @@ VarArrayBuffer::VarArrayBuffer(const Var& var) : Var(var) {
 }
 
 VarArrayBuffer::VarArrayBuffer(uint32_t size_in_bytes) {
-  if (has_interface<PPB_VarArrayBuffer_1_0>()) {
-    var_ = get_interface<PPB_VarArrayBuffer_1_0>()->Create(size_in_bytes);
-  } else {
-    PP_NOTREACHED();
-    var_ = PP_MakeNull();
-  }
-  is_managed_ = true;
+  ConstructWithSize(size_in_bytes);
 }
 
 pp::VarArrayBuffer& VarArrayBuffer::operator=(const VarArrayBuffer& other) {
@@ -74,4 +72,17 @@ void VarArrayBuffer::Unmap() {
     PP_NOTREACHED();
 }
 
+
+void VarArrayBuffer::ConstructWithSize(uint32_t size_in_bytes) {
+  PP_DCHECK(is_undefined());
+
+  if (has_interface<PPB_VarArrayBuffer_1_0>()) {
+    var_ = get_interface<PPB_VarArrayBuffer_1_0>()->Create(size_in_bytes);
+  } else {
+    PP_NOTREACHED();
+    var_ = PP_MakeNull();
+  }
+  is_managed_ = true;
+}
+
 }  // namespace pp