update setAnalysisRoots to accept package spec file

pkg/analysis_server/doc/api.html

Index: pkg/analysis_server/doc/api.html
diff --git a/pkg/analysis_server/doc/api.html b/pkg/analysis_server/doc/api.html
index f2c4df22ab9073bd36f49a8d42533a7b341058a9..fd1e1ef7b2e8e5597b659012bec18e168c83a796 100644
--- a/pkg/analysis_server/doc/api.html
+++ b/pkg/analysis_server/doc/api.html
@@ -757,17 +757,28 @@ dt.typeDefinition {
           </dd><dt class="field"><b><i>packageRoots ( <span style="color:#999999">optional</span> Map&lt;<a href="#type_FilePath">FilePath</a>, <a href="#type_FilePath">FilePath</a>&gt; )</i></b></dt><dd>
             
             <p>
-              A mapping from source directories to target directories
+              A mapping from source directories to package roots
               that should override the normal package: URI resolution
-              mechanism.  The analyzer will behave as though each
+              mechanism.
+            </p>
+            <p>
+              If a package root is a directory, then
+              the analyzer will behave as though the associated
               source directory in the map contains a special
               pubspec.yaml file which resolves any package: URI to the
-              corresponding path within the target directory.  The
-              effect is the same as specifying the target directory as
+              corresponding path within that package root directory.  The
+              effect is the same as specifying the package root directory as
               a "--package_root" parameter to the Dart VM when
               executing any Dart file inside the source directory.
             </p>
             <p>
+              If a package root is a file, then the analyzer
+              will behave as though that file is a ".packages" file in the
+              source directory. The effect is the same as specifying the file
+              as a "--packages" parameter to the Dart VM when
+              executing any Dart file inside the source directory.
+            </p>
+            <p>
               Files in any directories that are not overridden by this
               mapping have their package: URI's resolved using the
               normal pubspec.yaml mechanism.  If this field is absent,