Make popup menus line up to their baseline per the Material spec.

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.
 
@@ skipping 69 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.
+If a flow control structure's statement is one line long, then don't
+use braces around it. (Keeping the code free of boilerplate or
+redundant punctuation keeps it concise and readable.)
 
 > For example,
 > ```dart
->   if (children != null)
+>   if (children != null) {
 >     for (RenderBox child in children)
 >       add(child);
+>   }
 > ```
 > ...rather than:
 > ```dart
 >   if (children != null) {
 >     for (RenderBox child in children) {
 >       add(child);
 >     }
 >   }
 > ```
 
@@ skipping 17 matching lines @@
 
 C++
 ---
 
 Put spaces around operators in expressions.
 
 
 Java
 ----