Fix more -Wsign-compare warnings in heap, mips, base, etc.

test/cctest/test-global-handles.cc

Index: test/cctest/test-global-handles.cc
diff --git a/test/cctest/test-global-handles.cc b/test/cctest/test-global-handles.cc
index d777432f2fe178278d80ac28b86c78d0747d5fe9..256b74c6164a54f0d633179bfc37f4d0f10c195d 100644
--- a/test/cctest/test-global-handles.cc
+++ b/test/cctest/test-global-handles.cc
@@ -467,8 +467,8 @@ TEST(PhatomHandlesWithoutCallbacks) {
     g2.SetWeak();
   }
 
-  CHECK_EQ(0, isolate->NumberOfPhantomHandleResetsSinceLastCall());
+  CHECK_EQ(0u, isolate->NumberOfPhantomHandleResetsSinceLastCall());
   CcTest::CollectAllAvailableGarbage();
-  CHECK_EQ(2, isolate->NumberOfPhantomHandleResetsSinceLastCall());
-  CHECK_EQ(0, isolate->NumberOfPhantomHandleResetsSinceLastCall());
+  CHECK_EQ(2u, isolate->NumberOfPhantomHandleResetsSinceLastCall());
+  CHECK_EQ(0u, isolate->NumberOfPhantomHandleResetsSinceLastCall());
 }