dart2js: Inline across deferred output units if that leads to reduced size.

pkg/compiler/lib/src/deferred_load.dart

Index: pkg/compiler/lib/src/deferred_load.dart
diff --git a/pkg/compiler/lib/src/deferred_load.dart b/pkg/compiler/lib/src/deferred_load.dart
index b4ef154f4a0e134a4ebbe6326991f26ff048c9fe..2cd08666d72248d7548290bca9c27f852bba9bca 100644
--- a/pkg/compiler/lib/src/deferred_load.dart
+++ b/pkg/compiler/lib/src/deferred_load.dart
@@ -201,9 +201,20 @@ class DeferredLoadTask extends CompilerTask {
     return outputUnitForElement(element) != mainOutputUnit;
   }
 
-  /// Returns true if e1 and e2 are in the same output unit.
-  bool inSameOutputUnit(Element e1, Element e2) {
-    return outputUnitForElement(e1) == outputUnitForElement(e2);
+  /// Returns `true` if element [to] is reachable from element [from] without
+  /// crossing a deferred import.
+  ///
+  /// For example, if we have two deferred libraries `A` and `B` that both
+  /// import a library `C`, then even though elements from `A` and `C` end up in
+  /// different output units, there is a non-deferred path between `A` and `C`.
+  bool hasOnlyNonDeferredImportPaths(Element from, Element to) {
+    OutputUnit outputUnitFrom = outputUnitForElement(from);
+    OutputUnit outputUnitTo = outputUnitForElement(to);
+    return outputUnitTo.imports.containsAll(outputUnitFrom.imports);
+  }
+
+  bool isFromMainOutputUnit(Element element) {
+    return outputUnitForElement(element) == mainOutputUnit;
   }
 
   void registerConstantDeferredUse(DeferredConstantValue constant,