1. Figure out the modified libraries from the specifeid kernel file during

runtime/vm/kernel_reader.cc

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/kernel_reader.h"
 
 #include <string.h>
 
 #include "vm/dart_api_impl.h"
 #include "vm/kernel_binary.h"
@@ skipping 193 matching lines @@
   }
 
   // Either class finalization failed or we caught a compile error.
   // In both cases sticky error would be set.
   Error& error = Error::Handle(Z);
   error = thread_->sticky_error();
   thread_->clear_sticky_error();
   return error;
 }
 
+void KernelReader::FindModifiedLibraries(Isolate* isolate,
+                                         BitVector* modified_libs,
+                                         bool force_reload) {
+  LongJumpScope jump;
+  if (setjmp(*jump.Set()) == 0) {
+    if (force_reload) {
+      // If a reload is being forced we mark all libraries as having
+      // been modified.
+      const GrowableObjectArray& libs =
+          GrowableObjectArray::Handle(isolate->object_store()->libraries());
+      intptr_t num_libs = libs.Length();
+      Library& lib = dart::Library::Handle(Z);
+      for (intptr_t i = 0; i < num_libs; i++) {
+        lib ^= libs.At(i);
+        if (!lib.is_dart_scheme()) {
+          modified_libs->Add(lib.index());
+        }
+      }
+      return;
+    }
+    // Now go through all the libraries that are present in the incremental
+    // kernel files, these will constitute the modified libraries.
+    intptr_t length = program_->library_count();
+    for (intptr_t i = 0; i < length; i++) {
+      intptr_t kernel_offset = library_offset(i);
+      builder_.SetOffset(kernel_offset);
+      LibraryHelper library_helper(&builder_);
+      library_helper.ReadUntilIncluding(LibraryHelper::kCanonicalName);
+      dart::Library& lib = LookupLibrary(library_helper.canonical_name_);
+      if (!lib.IsNull() && !lib.is_dart_scheme()) {
+        // This is a library that already exists so mark it as being modified.
+        modified_libs->Add(lib.index());
+      }
+    }
+  }
+}
+
 void KernelReader::ReadLibrary(intptr_t kernel_offset) {
   builder_.SetOffset(kernel_offset);
   LibraryHelper library_helper(&builder_);
   library_helper.ReadUntilIncluding(LibraryHelper::kCanonicalName);
   Library& library = LookupLibrary(library_helper.canonical_name_);
   if (library.Loaded()) return;
 
   library_helper.ReadUntilIncluding(LibraryHelper::kName);
   library.SetName(H.DartSymbol(library_helper.name_index_));
 
@@ skipping 742 matching lines @@
   initializer_fun.set_result_type(AbstractType::Handle(zone, field.type()));
   initializer_fun.set_is_debuggable(false);
   initializer_fun.set_is_reflectable(false);
   initializer_fun.set_is_inlinable(false);
   return new (zone) ParsedFunction(thread, initializer_fun);
 }
 
 }  // namespace kernel
 }  // namespace dart
 #endif  // !defined(DART_PRECOMPILED_RUNTIME)