Simplify constructors translation, improve code style.

Simplify constructors translation, improve code style.

This CL stops generating and using "_impl" methods with constructor implementation.
This is actually required only locally, when there are other statements aside of redirecting constructor invocation.
So, this may be done later, during constructors optimizing in ConstructorSemanticProcessor.
For now we just transform placeholder of redirecting constructor invocation into the actual initializer.

Also, this CL adds more optimizations into ConstructorSemanticProcessor, such as:
1. removing empty constructor body;
2. enum constructor tweaks.

Plus new snapshot of analyzer_experimental with these changes in translation applied.

R=brianwilkerson@google.com
BUG=

Committed: https://code.google.com/p/dart/source/detail?r=24701

[Brian Wilkerson, 2013-07-02 14:21:45]

LGTM. The resulting code is *much* cleaner!

https://codereview.chromium.org/18129004/diff/1/editor/util/plugins/com.googl...
File
editor/util/plugins/com.google.dart.java2dart_test/src/com/google/dart/java2dart/SemanticTest.java
(right):

https://codereview.chromium.org/18129004/diff/1/editor/util/plugins/com.googl...
editor/util/plugins/com.google.dart.java2dart_test/src/com/google/dart/java2dart/SemanticTest.java:790:
// TODO(scheglov)
Is there still something to be done here?

[scheglov, 2013-07-02 17:45:28]

Committed patchset #1 manually as r24701 (presubmit successful).