First try to find the exact library for the given file URI.

pkg/analyzer/test/generated/all_the_rest_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.test.generated.all_the_rest_test;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
@@ skipping 158 matching lines @@
   void test_fromFile_library() {
     DirectoryBasedDartSdk sdk = _createDartSdk();
     Source source = sdk.fromFileUri(new JavaFile.relative(
             new JavaFile.relative(sdk.libraryDirectory, "core"), "core.dart")
         .toURI());
     expect(source, isNotNull);
     expect(source.isInSystemLibrary, isTrue);
     expect(source.uri.toString(), "dart:core");
   }
 
+  void test_fromFile_library_firstExact() {
+    DirectoryBasedDartSdk sdk = _createDartSdk();
+    JavaFile dirHtml = new JavaFile.relative(sdk.libraryDirectory, "html");
+    JavaFile dirDartium = new JavaFile.relative(dirHtml, "dartium");
+    JavaFile file = new JavaFile.relative(dirDartium, "html_dartium.dart");
+    expect(file.isFile(), isTrue);
+    Source source = sdk.fromFileUri(file.toURI());
+    expect(source, isNotNull);
+    expect(source.isInSystemLibrary, isTrue);
+    expect(source.uri.toString(), "dart:html");
+  }
+
   void test_fromFile_part() {
     DirectoryBasedDartSdk sdk = _createDartSdk();
     Source source = sdk.fromFileUri(new JavaFile.relative(
             new JavaFile.relative(sdk.libraryDirectory, "core"), "num.dart")
         .toURI());
     expect(source, isNotNull);
     expect(source.isInSystemLibrary, isTrue);
     expect(source.uri.toString(), "dart:core/num.dart");
   }
 
@@ skipping 3915 matching lines @@
     expect(UriKind.fromEncoding(0x70), same(UriKind.PACKAGE_URI));
     expect(UriKind.fromEncoding(0x58), same(null));
   }
 
   void test_getEncoding() {
     expect(UriKind.DART_URI.encoding, 0x64);
     expect(UriKind.FILE_URI.encoding, 0x66);
     expect(UriKind.PACKAGE_URI.encoding, 0x70);
   }
 }