rewrite_to_chrome_style: Use constexpr as backdoor to get consistency

In the last cases of inconsistent evaluation of compile-time-constants
just make them constexpr and then ensure we always see constexpr things
as compile-time constants. Actually compiling figures this out even
though from the AST we see unresolved things that make this hard.

R=dcheng
BUG=677285

Review-Url: https://codereview.chromium.org/2626923004
Cr-Commit-Position: refs/heads/master@{#443115}

third_party/WebKit/Source/platform/heap/TraceTraits.h

@@ -690,9 +690,9 @@ struct TraceInCollectionTrait<WeakHandlingInCollections,
     // key-value entry is leaked.  To avoid unexpected leaking, we disallow
     // this case, but if you run into this assert, please reach out to Blink
     // reviewers, and we may relax it.
-    const bool keyIsWeak =
+    constexpr bool keyIsWeak =
         Traits::KeyTraits::weakHandlingFlag == WeakHandlingInCollections;
-    const bool valueIsWeak =
+    constexpr bool valueIsWeak =
         Traits::ValueTraits::weakHandlingFlag == WeakHandlingInCollections;
     const bool keyHasStrongRefs =
         IsTraceableInCollectionTrait<typename Traits::KeyTraits>::value;

tools/clang/rewrite_to_chrome_style/RewriteToChromeStyle.cpp

@@ -475,6 +475,9 @@ bool IsProbablyConst(const clang::VarDecl& decl,
   if (type.isVolatileQualified())
     return false;
 
+  if (decl.isConstexpr())
+    return true;
+
   // Parameters should not be renamed to |kFooBar| style (even if they are
   // const and have an initializer (aka default value)).
   if (clang::isa<clang::ParmVarDecl>(&decl))