build(aio): left align code regions

aio/transforms/examples-package/services/region-parser.js

@@ -103,7 +103,7 @@ function regionParserImpl(contents, fileType) {
     }
     return {
       contents: lines.join('\n'),
-      regions: mapObject(regionMap, (regionName, region) => region.lines.join('\n'))
+      regions: mapObject(regionMap, (regionName, region) => leftAlign(region.lines).join('\n'))
     };
   } else {
     return {contents, regions: {}};
@@ -119,6 +119,17 @@ function removeLast(array, item) {
   array.splice(index, 1);
 }
 
+function leftAlign(lines) {
+  let indent = Number.MAX_VALUE;
+  lines.forEach(line => {
+    const lineIndent = line.search(/\S/);
+    if (lineIndent !== -1) {
+      indent = Math.min(lineIndent, indent);
+    }
+  });
+  return lines.map(line => line.substr(indent));
+}
+
 function RegionParserError(message, index) {
   const lineNum = index + 1;
   this.message = `regionParser: ${message} (at line ${lineNum}).`;

aio/transforms/examples-package/services/region-parser.spec.js

@@ -43,6 +43,17 @@ describe('regionParser service', () => {
     expect(output.contents).toEqual(t('abc', 'def', 'ghi'));
   });
 
+  it('should left align the text of the region', () => {
+    const output = regionParser(
+      t(
+        '/* #docregion X */', '  all', '    indented', '    by', '  two', '  spaces', '/* #enddocregion X */',
+        '/* #docregion Y */', '    first', '  line', '  indented', '    more', '  than', '  later', '  lines', '/* #enddocregion Y */',
+        '/* #docregion Z */', '  ignore', '  ', '  empty', '', '  lines', '/* #enddocregion Z */'
+      ), 'test-type');
+    expect(output.regions['X']).toEqual(t('all', '  indented', '  by', 'two', 'spaces'));
+    expect(output.regions['Y']).toEqual(t('  first', 'line', 'indented', '  more', 'than', 'later', 'lines'));
+    expect(output.regions['Z']).toEqual(t('ignore', '', 'empty', '', 'lines'));
+  });
 
   it('should remove doc plaster annotations from the contents', () => {
     const output =