extend unstable API to pass in the location of the libraries-specification

For now I'm just passing null, in a future CL I will pass a valid library
specification uri. This is needed in order to provide a library specification
that fasta will use to determine the result of a config-specific import.

Change-Id: I5e6babb0eb11bd1037262ea1260bc67188ef4649
Reviewed-on: https://dart-review.googlesource.com/47405
Commit-Queue: Sigmund Cherem <sigmund@google.com>
Reviewed-by: Peter von der Ahé <ahe@google.com>
diff --git a/pkg/compiler/lib/src/library_loader.dart b/pkg/compiler/lib/src/library_loader.dart
index e6e2ea8..378ca10 100644
--- a/pkg/compiler/lib/src/library_loader.dart
+++ b/pkg/compiler/lib/src/library_loader.dart
@@ -868,6 +868,7 @@
         initializedCompilerState = fe.initializeCompiler(
             initializedCompilerState,
             new Dart2jsTarget(new TargetFlags(strongMode: strongMode)),
+            null,
             platformBinaries.resolve(platform),
             _packageConfig);
         component = await fe.compile(
diff --git a/pkg/front_end/lib/src/api_unstable/dart2js.dart b/pkg/front_end/lib/src/api_unstable/dart2js.dart
index c8151c0..666f32d 100644
--- a/pkg/front_end/lib/src/api_unstable/dart2js.dart
+++ b/pkg/front_end/lib/src/api_unstable/dart2js.dart
@@ -27,18 +27,24 @@
 
 export 'compiler_state.dart' show InitializedCompilerState;
 
-InitializedCompilerState initializeCompiler(InitializedCompilerState oldState,
-    Target target, Uri sdkUri, Uri packagesFileUri) {
+InitializedCompilerState initializeCompiler(
+    InitializedCompilerState oldState,
+    Target target,
+    Uri librariesSpecificationUri,
+    Uri sdkPlatformUri,
+    Uri packagesFileUri) {
   if (oldState != null &&
       oldState.options.packagesFileUri == packagesFileUri &&
-      oldState.options.linkedDependencies[0] == sdkUri) {
+      oldState.options.librariesSpecificationUri == librariesSpecificationUri &&
+      oldState.options.linkedDependencies[0] == sdkPlatformUri) {
     return oldState;
   }
 
   CompilerOptions options = new CompilerOptions()
     ..target = target
     ..strongMode = target.strongMode
-    ..linkedDependencies = [sdkUri]
+    ..linkedDependencies = [sdkPlatformUri]
+    ..librariesSpecificationUri = librariesSpecificationUri
     ..packagesFileUri = packagesFileUri;
 
   ProcessedOptions processedOpts = new ProcessedOptions(options, false, []);