Move interpreter cctests into v8::internal::interpreter namespace.

This moves the cctest file for the interpreter to live in the same
namespace as the components it is testing. Hence we can avoid the
forbidden using directives pulling in entire namespaces.

From the Google C++ style guide: "You may not use a using-directive to
make all names from a namespace available". This would be covered by
presubmit linter checks if build/namespaces were not blacklisted.

R=rmcilroy@chromium.org

Review URL: https://codereview.chromium.org/1410993009

Cr-Commit-Position: refs/heads/master@{#31681}

test/cctest/interpreter/test-interpreter.cc

@@ -155,19 +155,6 @@ class InterpreterTester {
   DISALLOW_COPY_AND_ASSIGN(InterpreterTester);
 };
 
-}  // namespace interpreter
-}  // namespace internal
-}  // namespace v8
-
-using v8::internal::BytecodeArray;
-using v8::internal::Handle;
-using v8::internal::LanguageMode;
-using v8::internal::Object;
-using v8::internal::Runtime;
-using v8::internal::Smi;
-using v8::internal::Strength;
-using v8::internal::Token;
-using namespace v8::internal::interpreter;
 
 TEST(InterpreterReturn) {
   HandleAndZoneScope handles;
@@ -2724,3 +2711,7 @@ TEST(InterpreterForIn) {
     CHECK_EQ(Handle<Smi>::cast(return_val)->value(), for_in_samples[i].second);
   }
 }
+
+}  // namespace interpreter
+}  // namespace internal
+}  // namespace v8