6952330: Fix for 6933217 broke contract of StringBuffer.ensureCapacity
Summary: make sure to grow with size => size * 2 + 2
Reviewed-by: dholmes, chegar, ohair
^build/
^dist/
/nbproject/private/
^src/share/tools/hsdis/build/
^src/share/tools/IdealGraphVisualizer/[a-zA-Z0-9]*/build/
^src/share/tools/IdealGraphVisualizer/build/
^src/share/tools/IdealGraphVisualizer/dist/