Make patch file import declarations apply to the patched library too.

lib/compiler/implementation/compiler.dart

Index: lib/compiler/implementation/compiler.dart
diff --git a/lib/compiler/implementation/compiler.dart b/lib/compiler/implementation/compiler.dart
index c0f70bac3a7f6ac3fc4c11034453cb956806460c..3665544da58429146181abb7611439757bcfd848 100644
--- a/lib/compiler/implementation/compiler.dart
+++ b/lib/compiler/implementation/compiler.dart
@@ -269,7 +269,11 @@ class Compiler implements DiagnosticListener {
       // do not have enough stack space.
       throw;
     } catch (var ex) {
-      unhandledExceptionOnElement(element);
+      try {
+        unhandledExceptionOnElement(element);
+      } catch (var doubleFault) {
+        // Ignoring exceptions in exception handling.
+      }
       throw;
     } finally {
       _currentElement = old;
@@ -525,6 +529,10 @@ class Compiler implements DiagnosticListener {
   }
 
   void applyLibraryPatch(LibraryElement library, LibraryElement patch) {
+    // We allow foreign functions in patched libraries.
+    addForeignFunctions(library);  // Is safe even if already added.
+
+    // Copy/patch top-level elements.
     Link<Element> patches = patch.topLevelElements;
     while (!patches.isEmpty()) {
       Element patchElement = patches.head;
@@ -548,7 +556,29 @@ class Compiler implements DiagnosticListener {
       }
       patches = patches.tail;
     }
+
+    // Copy imports.
+    Map<String, LibraryElement> delayedPatches = <LibraryElement>{};
+    Uri base = patch.script.uri;
+    for (ScriptTag tag in patch.tags.reverse()) {
+      if (tag.isImport()) {
+        StringNode argument = tag.argument;
+        Uri resolved = base.resolve(argument.dartString.slowToString());
+        LibraryElement importedLibrary =
+            scanner.loadLibrary(resolved, argument);
+        scanner.importLibrary(library, importedLibrary, tag, patch);
+        if (resolved.scheme == "dart") {
+          delayedPatches[resolved.path] = importedLibrary;
+        }
+      }
+    }
+    // Mark library as already patched.
     library.patch = patch;
+    // We patch imported libraries after marking the current library as patched,
+    // to avoid problems with cyclic dependencies.
+    delayedPatches.forEach((String path, LibraryElement importedLibrary) {
+      patchDartLibrary(importedLibrary, path);
+    });
   }
 
   bool patchSignatureMatches(FunctionElement original, FunctionElement patch) {