Get rid of DART_SDK in pub.

sdk/lib/_internal/pub/lib/src/sdk.dart

Index: sdk/lib/_internal/pub/lib/src/sdk.dart
diff --git a/sdk/lib/_internal/pub/lib/src/sdk.dart b/sdk/lib/_internal/pub/lib/src/sdk.dart
index 65aaef6077c543e3a69014e73311fa963e072898..c99f516a3a57077265bba483aa0854240612d470 100644
--- a/sdk/lib/_internal/pub/lib/src/sdk.dart
+++ b/sdk/lib/_internal/pub/lib/src/sdk.dart
@@ -10,7 +10,6 @@ import 'dart:io';
 import 'package:path/path.dart' as path;
 
 import 'io.dart';
-import 'log.dart' as log;
 import 'version.dart';
 
 /// Matches an Eclipse-style SDK version number. This is four dotted numbers
@@ -20,19 +19,14 @@ final _versionPattern = new RegExp(r'^(\d+)\.(\d+)\.(\d+)\.(\d+.*)$');
 
 /// Gets the path to the root directory of the SDK.
 String get rootDirectory {
-  // If the environment variable was provided, use it. This is mainly used for
-  // the pub tests.
-  var dir = Platform.environment["DART_SDK"];
-  if (dir != null) {
-    log.fine("Using DART_SDK to find SDK at $dir");
-    return dir;
-  }
-
   // Assume the Dart executable is always coming from the SDK.
   return path.dirname(path.dirname(Platform.executable));
 }
 
-/// Gets the SDK's revision number formatted to be a semantic version.
+/// The SDK's revision number formatted to be a semantic version.
+///
+/// This can be set so that the version solver tests can artificially select
+/// different SDK versions.
 Version version = _getVersion();
 
 /// Is `true` if the current SDK is an unreleased bleeding edge version.
@@ -41,11 +35,8 @@ bool get isBleedingEdge {
   return version.major == 0 && version.minor == 1 && version.patch == 2;
 }
 
-/// Determine the SDK's version number.
-Version _getVersion() {
-  var revisionPath = path.join(rootDirectory, "version");
-  var version = readTextFile(revisionPath).trim();
-
+/// Parse an Eclipse-style version number using the SDK's versioning convention.
+Version parseVersion(String version) {
   // Given a version file like: 0.1.2.0_r17495
   // We create a semver like:   0.1.2+0.r17495
   var match = _versionPattern.firstMatch(version);
@@ -61,3 +52,17 @@ Version _getVersion() {
       int.parse(match[1]), int.parse(match[2]), int.parse(match[3]),
       build: build);
 }
+
+/// Determine the SDK's version number.
+Version _getVersion() {
+  // Some of the pub integration tests require an SDK version number, but the
+  // tests on the bots are not run from a built SDK so this lets us avoid
+  // parsing the missing version file.
+  var sdkVersion = Platform.environment["_PUB_TEST_SDK_VERSION"];
+  if (sdkVersion != null) return new Version.parse(sdkVersion);
+
+  // Read the "version" file.
+  var revisionPath = path.join(rootDirectory, "version");
+  var version = readTextFile(revisionPath).trim();
+  return parseVersion(version);
+}