title: Flutter : "Could not resolved the package" every install new packages
body: <p>I have some problem about installing new package from pub.dev. I create my own package inside my root project with this command :</p>
  <p><code>flutter create --template=package main_template</code></p>
  <h2>structure folder</h2>
  <p><a href="https://i.stack.imgur.com/6saCD.png" rel="noreferrer"><img src="https://i.stack.imgur.com/6saCD.png" alt="Structure folder" /></a></p>
  <p>I installing new package inside <strong>main_template</strong> not <strong>lib</strong>. every install new package in <strong>main_template</strong> i received this error :</p>
  <pre><code>
  Compiler message:
  Error: Could not resolve the package 'device_info' in 'package:device_info/device_info.dart'.
  sinergi_flutter_template/main_template/lib/variable/get_device_id.dart:3:8: Error: Not found: 'package:device_info/device_info.dart'
  import 'package:device_info/device_info.dart';
         ^
  sinergi_flutter_template/main_template/lib/variable/get_device_id.dart:9:11: Error: 'DeviceInfoPlugin' isn't a type.
      final DeviceInfoPlugin deviceInfoPlugin = DeviceInfoPlugin();
            ^^^^^^^^^^^^^^^^
  sinergi_flutter_template/main_template/lib/variable/get_device_id.dart:9:47: Error: The method 'DeviceInfoPlugin' isn't defined for the class 'GetDeviceId'.
   - 'GetDeviceId' is from 'package:main_template/variable/get_device_id.dart' ('sinergi_flutter_template/main_template/lib/variable/get_device_id.dart').
  Try correcting the name to the name of an existing method, or defining a method named 'DeviceInfoPlugin'.
      final DeviceInfoPlugin deviceInfoPlugin = DeviceInfoPlugin();
                                                ^^^^^^^^^^^^^^^^
  U
  nhandled exception:
  FileSystemException(uri=org-dartlang-u
  ntranslatable-uri:package%3Adevice_info%2Fdevice_info.dart; message=StandardFileSystem only supports file:* and data:* URIs)
  #0      StandardFileSystem.entityForUri  (package:front_end/src/api_prototype/standard_file_system.dart:33:7)
  #1      asFileUri ( (package:vm/kernel_front_end.dart:604:3)
  7)
  #2      writeDepfile  (package:vm/kernel_front_end.dart:799:21)
  &lt;asynchronous suspension&gt;
  #3      FrontendCompiler.compile  (package:frontend_server/frontend_server.dart:472:15)
  &lt;asynchronous suspension&gt;
  #4      _FlutterFrontendCompiler.compile (package:flut
  ter_frontend_server/server.dart:38:22)
  #5      starter  (package:flutter_frontend_server/server.dart:149:27)
  #6      main  (file:///C:/b/s/w/ir/cache/builder/src/flutter/flutter_frontend_server/bin/starter.dart:8:30)
  #7      _startIsolate.&lt;anonymous closure&gt;  (dart:isolate-patch/isolate_patch.dart:305:32)
  #8      _RawReceivePortImpl._handleMessage  (dart:isolate-patch/isolate_patch.dart:174:12)
  Target kernel_snapshot failed: Exception: Errors during snapshot creation: null
  build failed.
  
  FAILURE: Build failed with an exception.
  
  * Where:
  Script 'C:\flutter\flutter\packages\flutter_tools\gradle\flutter.gradle' line: 780
  
  * What went wrong:
  Execution failed for task ':app:compileFlutterBuildDebug'.
  &gt; Process 'command 'C:\flutter\flutter\bin\flutter.bat'' finished with non-zero exit value 1
  
  * Try:
  Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
  
  * Get more help at https://help.gradle.org
  
  BUILD FAILED in 20s
  Gradle task assembleDebug failed with exit code 1
  Exited (sigterm)
  
  </code></pre>
  <blockquote>
  <p>Until now i trying install 3 package [Cache Network Image,Device Info , SplashScreen]. And all packages give me that error.</p>
  </blockquote>
  <p>How can i fixed it ?</p>