Fix some leaks and failures under valgrind in JS extensions unit tests.

extensions/renderer/module_system_test.cc

Index: extensions/renderer/module_system_test.cc
diff --git a/extensions/renderer/module_system_test.cc b/extensions/renderer/module_system_test.cc
index 4f4675e625610be86972476ac2dca54fd4e68d07..aa6480f65837bd88d213bb9ba54f84950475b701 100644
--- a/extensions/renderer/module_system_test.cc
+++ b/extensions/renderer/module_system_test.cc
@@ -209,18 +209,33 @@ v8::Handle<v8::Object> ModuleSystemTestEnvironment::CreateGlobal(
 
 ModuleSystemTest::ModuleSystemTest()
     : isolate_(v8::Isolate::GetCurrent()),
-      env_(CreateEnvironment()),
       should_assertions_be_made_(true) {
 }
 
 ModuleSystemTest::~ModuleSystemTest() {
 }
 
+void ModuleSystemTest::SetUp() {
+  env_ = CreateEnvironment();
+}
+
 void ModuleSystemTest::TearDown() {
   // All tests must assert at least once unless otherwise specified.
   EXPECT_EQ(should_assertions_be_made_,
             env_->assert_natives()->assertion_made());
   EXPECT_FALSE(env_->assert_natives()->failed());
+  env_.reset();
+  v8::HeapStatistics stats;
+  isolate_->GetHeapStatistics(&stats);
+  size_t old_heap_size = 0;
+  // Run the GC until the heap size reaches a steady state to ensure that
+  // all the garbage is collected.
+  while (stats.used_heap_size() != old_heap_size) {
+    old_heap_size = stats.used_heap_size();
+    isolate_->RequestGarbageCollectionForTesting(
+        v8::Isolate::kFullGarbageCollection);
+    isolate_->GetHeapStatistics(&stats);
+  }
 }
 
 scoped_ptr<ModuleSystemTestEnvironment> ModuleSystemTest::CreateEnvironment() {