Minor refactorings to use some recently added methods.

src/compilation-cache.cc

Index: src/compilation-cache.cc
diff --git a/src/compilation-cache.cc b/src/compilation-cache.cc
index 9dcbeb5eeba130b1929d5253038dcf0b438e4917..378a24e7504e2ae8bcf836d2487d391747f3a1ae 100644
--- a/src/compilation-cache.cc
+++ b/src/compilation-cache.cc
@@ -218,9 +218,7 @@ void CompilationSubCache::Iterate(ObjectVisitor* v) {
 
 
 void CompilationSubCache::Clear() {
-  for (int i = 0; i < generations_; i++) {
-    tables_[i] = Heap::undefined_value();
-  }
+  MemsetPointer(tables_, Heap::undefined_value(), generations_);
 }