Stop running pub get at gclient sync time and fix build bugs

mojo/public/dart/third_party/shelf_static/CHANGELOG.md

Index: mojo/public/dart/third_party/shelf_static/CHANGELOG.md
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+## 0.2.3+1
+
+* Support `http_parser` 1.0.0.
+
+## 0.2.3
+
+* Added `listDirectories` argument to `createStaticHandler`. 
+
+## 0.2.2
+
+* Bumped up minimum SDK to 1.7.0.
+
+* Added support for `shelf` 0.6.0.
+
+## 0.2.1
+
+* Removed `Uri` format checks now that the core libraries is more strict. 
+
+## 0.2.0
+
+* Removed deprecated `getHandler`.
+
+* Send correct mime type for default document.
+
+## 0.1.4+6
+
+* Updated development dependencies.
+
+## 0.1.4+5
+
+* Handle differences in resolution between `DateTime` and HTTP date format.
+
+## 0.1.4+4
+
+* Using latest `shelf`. Cleaned up test code by using new features.
+
+## 0.1.4
+
+* Added named (optional) `defaultDocument` argument to `createStaticHandler`.
+
+## 0.1.3
+
+* `createStaticHandler` added `serveFilesOutsidePath` optional parameter.
+
+## 0.1.2
+
+* The preferred top-level method is now `createStaticHandler`. `getHandler` is deprecated.
+* Set `content-type` header if the mime type of the requested file can be determined from the file extension.
+* Respond with `304-Not modified` against `IF-MODIFIED-SINCE` request header.
+* Better error when provided a non-existant `fileSystemPath`.
+* Added `example/example_server.dart`.
+
+## 0.1.1+1
+
+* Removed work around for [issue](https://codereview.chromium.org/278783002/).
+
+## 0.1.1
+
+* Correctly handle requests when not hosted at the root of a site.
+* Send `last-modified` header.
+* Work around [known issue](https://codereview.chromium.org/278783002/) with HTTP date formatting.