Copy ICData descriptors when starting background compilation, so that they do not change while comp…

runtime/vm/compiler_test.cc

Index: runtime/vm/compiler_test.cc
diff --git a/runtime/vm/compiler_test.cc b/runtime/vm/compiler_test.cc
index a231839e553e2f70160b3c12528bc6480ceba90f..03ef98ff45afb5b03a3e616c3f3faccb156b5f14 100644
--- a/runtime/vm/compiler_test.cc
+++ b/runtime/vm/compiler_test.cc
@@ -14,6 +14,8 @@
 
 namespace dart {
 
+DECLARE_FLAG(bool, background_compilation);
+
 TEST_CASE(CompileScript) {
   const char* kScriptChars =
       "class A {\n"
@@ -95,6 +97,7 @@ TEST_CASE(CompileFunctionOnHelperThread) {
   CompilerTest::TestCompileFunction(func);
   EXPECT(func.HasCode());
   EXPECT(!func.HasOptimizedCode());
+  FLAG_background_compilation = true;
   BackgroundCompiler::EnsureInit(thread);
   Isolate* isolate = thread->isolate();
   ASSERT(isolate->background_compiler() != NULL);