Change our editor tab spacing defaults to 2 spaces.

Change our editor tab spacing defaults to 2 spaces.
Committed: https://code.google.com/p/dart/source/detail?r=1713

[devoncarew, 2011-11-19 08:49:41]

Fix for http://code.google.com/p/dart/issues/detail?id=527.

[pquitslund, 2011-11-21 17:39:30]

LGTM w/a question...

http://codereview.chromium.org/8603011/diff/1/editor/tools/plugins/com.google...
File
editor/tools/plugins/com.google.dart.tools.ui/src/com/google/dart/tools/ui/text/DartSourceViewerConfiguration.java
(right):

http://codereview.chromium.org/8603011/diff/1/editor/tools/plugins/com.google...
editor/tools/plugins/com.google.dart.tools.ui/src/com/google/dart/tools/ui/text/DartSourceViewerConfiguration.java:634:
public int getTabWidth(ISourceViewer sourceViewer) {
2 is what we want to return for sure but I wonder if there isn't a better place
to set this.  IOW: can we get super.getTabWidth(sourceViewer); to do the right
thing?

[devoncarew, 2011-11-21 19:10:56]

http://codereview.chromium.org/8603011/diff/1/editor/tools/plugins/com.google...
File
editor/tools/plugins/com.google.dart.tools.ui/src/com/google/dart/tools/ui/text/DartSourceViewerConfiguration.java
(right):

http://codereview.chromium.org/8603011/diff/1/editor/tools/plugins/com.google...
editor/tools/plugins/com.google.dart.tools.ui/src/com/google/dart/tools/ui/text/DartSourceViewerConfiguration.java:634:
public int getTabWidth(ISourceViewer sourceViewer) {
The parent method pulls the value from the preferences defaults. We don't have
control over those defaults unfortunately; they're set in code that would not be
easy to change.

I pulled the constant value out into a constant ('TAB_WIDTH_IN_SPACES'). We can
look into integrating this constant with the formatter settings in the future,
so there are fewer magic constants floating around.