Add package root setting to analysis server API.

pkg/analysis_server/tool/spec/spec_input.html

Index: pkg/analysis_server/tool/spec/spec_input.html
diff --git a/pkg/analysis_server/tool/spec/spec_input.html b/pkg/analysis_server/tool/spec/spec_input.html
index b55d4fe71f5b06fa59f013894fb66096eb360660..cd267be0fba7d9a4d4d446be3b504d98348f4e03 100644
--- a/pkg/analysis_server/tool/spec/spec_input.html
+++ b/pkg/analysis_server/tool/spec/spec_input.html
@@ -389,6 +389,28 @@
               included directories that should not be analyzed.
             </p>
           </field>
+          <field name="packageRoots" optional="true">
+            <map>
+              <key><ref>FilePath</ref></key>
+              <value><ref>FilePath</ref></value>
+            </map>
+            <p>
+              A mapping from source directories to target directories
+              that should override the normal package: URI resolution
+              mechanism.  The analyzer will behave as though each
+              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
+              a "--package_root" parameter to the Dart VM when
+              executing any Dart file inside the source directory.
+            </p>
+            <p>
+              If this field is absent, or the empty map is specified,
+              then all package: URI's are resolved the normal

[Brian Wilkerson, 2014/10/22 20:57:08]

"resolved the" --> "resolved using the"

And I assume that package: URI's in files in directories that are not inside any
source directory are also resolved normally. Should we specify that explicitly?

[Paul Berry, 2014/10/23 00:09:01]

Done.
Yes, excluding pathological cases.  I've added text clarify this.

+              pubspec.yaml mechanism.
+            </p>
+          </field>
         </params>
       </request>
       <request method="setPriorityFiles">