chore(lint): Add lint check for license headers

Added a tslint check to make sure all source files begin with a license
header (at the very beginning or after a `#!`).

Relates to angular#9380

Author: ScottSWu

tools/tslint/enforceCopyrightHeaderRule.ts

@@ -0,0 +1,32 @@
+import {RuleWalker} from 'tslint/lib/language/walker';
+import {RuleFailure} from 'tslint/lib/lint';
+import {AbstractRule} from 'tslint/lib/rules';
+import * as ts from 'typescript';
+
+export class Rule extends AbstractRule {
+  public static FAILURE_STRING = 'missing copyright header';
+
+  public apply(sourceFile: ts.SourceFile): RuleFailure[] {
+    const walker = new EnforceCopyrightHeaderWalker(sourceFile, this.getOptions());
+    return this.applyWithWalker(walker);
+  }
+}
+
+class EnforceCopyrightHeaderWalker extends RuleWalker {
+  private regex: RegExp = /\/\*[\s\S]*?Copyright Google Inc\.[\s\S]*?\*\//;
+
+  public visitSourceFile(node: ts.SourceFile) {
+    // check for a shebang
+    let text = node.getFullText();
+    let offset = 0;
+    if (text.indexOf('#!') === 0) {
+      offset = text.indexOf('\n') + 1;
+      text = text.substring(offset);
+    }
+    // look for the copyright header
+    let match = text.match(this.regex);
+    if (!match || match.index !== 0) {
+      this.addFailure(this.createFailure(offset, offset + 1, Rule.FAILURE_STRING));
+    }
+  }
+}

tslint.json

@@ -2,6 +2,7 @@
     "rules": {
       "requireInternalWithUnderscore": true,
       "duplicateModuleImport": true,
+      "enforce-copyright-header": true,
       "semicolon": true,
       "variable-name": [true, "ban-keywords"]
     }