[test] Add paths to chrome and firefox to the environment when present

This adds a CHROME_PATH or FIREFOX_PATH environment variable to the
test's evnironment which contains a path to the browser's executable.
This is only set if the --chrome or --firefox argument was passed to
test.py.

#42417

Change-Id: I711de6ab91b8ffbbe72c7fb1530b68c4189a4b8a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/153209
Commit-Queue: Alexander Thomas <athom@google.com>
Reviewed-by: William Hesse <whesse@google.com>

Author: athomas

pkg/test_runner/lib/src/test_suite.dart

@@ -55,14 +55,16 @@ abstract class TestSuite {
   TestSuite(this.configuration, this.suiteName, this.statusFilePaths) {
     _environmentOverrides = {
       'DART_CONFIGURATION': configuration.configurationDirectory,
+      if (Platform.isWindows) 'DART_SUPPRESS_WER': '1',
+      if (Platform.isWindows && configuration.copyCoreDumps)
+        'DART_CRASHPAD_HANDLER':
+            Uri.base.resolve(buildDir + '/crashpad_handler.exe').toFilePath(),
+      if (configuration.chromePath != null)
+        'CHROME_PATH': Uri.base.resolve(configuration.chromePath).toFilePath(),
+      if (configuration.firefoxPath != null)
+        'FIREFOX_PATH':
+            Uri.base.resolve(configuration.firefoxPath).toFilePath(),
     };
-    if (Platform.isWindows) {
-      _environmentOverrides['DART_SUPPRESS_WER'] = '1';
-      if (configuration.copyCoreDumps) {
-        _environmentOverrides['DART_CRASHPAD_HANDLER'] =
-            Path(buildDir + '/crashpad_handler.exe').absolute.toNativePath();
-      }
-    }
   }
 
   Map<String, String> get environmentOverrides => _environmentOverrides;