Ignore all environment variables with name starting with '='

sdk/lib/io/platform_impl.dart

Index: sdk/lib/io/platform_impl.dart
diff --git a/sdk/lib/io/platform_impl.dart b/sdk/lib/io/platform_impl.dart
index 0cffec6a532bd98f77549122771e11297bec48ff..eaad98af995bdb3119f5e654ba2cd75d7d6b29e1 100644
--- a/sdk/lib/io/platform_impl.dart
+++ b/sdk/lib/io/platform_impl.dart
@@ -58,20 +58,29 @@ class _Platform {
         var isWindows = operatingSystem == 'windows';
         var result = isWindows ? new _CaseInsensitiveStringMap() : new Map();
         for (var str in env) {
-          // When running on Windows through cmd.exe there are strange
-          // environment variables that are used to record the current
-          // working directory for each drive and the exit code for the
-          // last command. As an example: '=A:=A:\subdir' records the
-          // current working directory on the 'A' drive.  In order to
-          // handle these correctly we search for a second occurrence of
-          // of '=' in the string if the first occurrence is at index 0.
+          // When running on Windows through cmd.exe there are
+          // entries which starts with '='. In CMD scripting,
+          // variables are "dynamic" environment variables which change
+          // automatically. The values of the ones starting with "=" are
+          // reified in the environment string of a new program (but, e.g.,
+          // __CD__ isn't).
+          //
+          // One example are the use of the environment to communicate the
+          // current working directory for each drive and the exit code for the
+          // last command. E.g. the entry '=A:=A:\subdir' records the current
+          // working directory on the 'A' drive.
+          //
+          // On Mac OS an entry of just '=' has been seen.
+          //
+          // Entries starting with '=' are ignored.
+          //
+          // Entries with no '=' should not happen. If it should happen,
+          // the entry is ignored.
           var equalsIndex = str.indexOf('=');
-          if (equalsIndex == 0) {
-            equalsIndex = str.indexOf('=', 1);
+          if (equalsIndex > 0) {
+            result[str.substring(0, equalsIndex)] =
+                str.substring(equalsIndex + 1);
           }
-          assert(equalsIndex != -1);
-          result[str.substring(0, equalsIndex)] =
-              str.substring(equalsIndex + 1);
         }
         _environmentCache = new UnmodifiableMapView<String, String>(result);
       } else {