Give rationale for style guide, suggest using more concise code when doing so doesn't harm readabil…

sky/specs/style-guide.md

 Sky Style Guide
 ===============
 
 In general, follow our [Design Principles](design.md) for all code.
 
+The primary goal of this style guide is to improve code readability so
+that everyone, whether reading the code for the first time or
+maintaining it for years, can quickly determine what the code does. A
+secondary goal is avoiding arguments when there are disagreements.
 
 Dart
 ----
 
 In general, follow the [Dart style
 guide](https://www.dartlang.org/articles/style-guide/) for Dart code,
 except where that would contradict this page.
 
 Always use the Dart Analyzer. Do not check in code that increases the
 output of the analyzer unless you've filed a bug with the Dart team.
@@ skipping 60 matching lines @@
 
 When breaking a parameter list into multiple lines, do the same.
 
 Use // and ///, not /* */ and /** */.
 
 Don't put the statement part of an "if" statement on the same line as
 the expression, even if it is short. (Doing so makes it unobvious that
 there is relevant code there. This is especially important for early
 returns.)
 
+If a flow control structure has just one statement, then don't use
+braces around it except where doing so would help readability or avoid
+the dangling-else problem. Keeping the code free of boilerplate or
+redundant punctuation keeps it concise and readable.
+
+> For example,
+> ```dart
+>   if (children != null)
+>     for (RenderBox child in children)
+>       add(child);

[abarth-chromium, 2015/06/25 17:17:12]

The usual Google style for this situation is to put a { } around a single
statement if that statement occupies more than one physical line.  For example,
this could would become:

if (children != null) {
  for (RenderBox child in children)
    add(child);
}

Because the body of the |if| takes up more than one physical line.

+> ```
+> ...rather than:
+> ```dart
+>   if (children != null) {
+>     for (RenderBox child in children) {
+>       add(child);
+>     }
+>   }
+> ```
+
 
 Use the most relevant constructor or method, when there are multiple
 options.
 
 > For example,
 > ```dart
 >    new EdgeDims.symmetric(horizontal: 8.0);
 > ```
 > ...rather than:
 > ```dart
 >    new EdgeDims(0.0, 8.0, 0.0, 8.0);
 > ```
 
 
 C++
 ---
 
 
 Java
 ----