[escher] Add a default constructor to buffer text view

Change-Id: Ic71b478f146591f2e93ca80722e1597eb05ccfdd

escher/include/escher/buffer_text_view.h

@@ -5,6 +5,7 @@
 
 class BufferTextView : public TextView {
 public:
+  BufferTextView();
   BufferTextView(float horizontalAlignment, float verticalAlignment,
     KDColor textColor = KDColorBlack, KDColor backgroundColor = KDColorWhite);
   void setText(const char * text);

escher/src/buffer_text_view.cpp

@@ -2,6 +2,11 @@
 #include <string.h>
 #include <assert.h>
 
+BufferTextView::BufferTextView() :
+  TextView(0.5f, 0.5f, KDColorBlack, KDColorWhite)
+{
+}
+
 BufferTextView::BufferTextView(float horizontalAlignment, float verticalAlignment,
     KDColor textColor, KDColor backgroundColor) :
   TextView(horizontalAlignment, verticalAlignment, textColor, backgroundColor)