build(gulp): turn off dartfmt logs by default

Closes #2105

tools/build/logging.js

@@ -0,0 +1,43 @@
+var kLogsArgument = /^--logs\s*=\s*(.+?)$/;
+var kTrimLeft = /^\s+/;
+var kTrimRight = /\s+$/;
+var kCamelCase = /[-_\s]+(.)?/g;
+var logs = findArgvLogs();
+
+function findArgvLogs() {
+  for (var i = 0; i < process.argv.length; ++i) {
+    var match = process.argv[i].match(kLogsArgument);
+    if (match) {
+      return logsToObject(match[1]);
+    }
+  }
+  return null;
+}
+
+function logsToObject(logstr) {
+  return logstr.
+    split(',').
+    reduce(function(obj, key) {
+      key = camelize(key);
+      if (key.length > 0) obj[key] = true;
+      return obj;
+    }, Object.create(null));
+  return logs;
+}
+
+function camelize(str) {
+  return str.
+    replace(kTrimLeft, '').
+    replace(kTrimRight, '').
+    replace(kCamelCase, function(match, c) {
+      return c ? c.toUpperCase() : "";
+    });
+}
+
+function shouldLog(str) {
+  if (!logs || logs.quiet) return false;
+  if (logs.all) return true;
+  return !!logs[camelize(str)];
+}
+
+module.exports = shouldLog;