rewrite_to_chrome_style: Make const decisions aware of const variables

When a const variable is initialized by another variable, we recurse
to see if that variable is compile-time-const to decide if the former
variable is.

BUG=677285

Review-Url: https://codereview.chromium.org/2624253002
Cr-Commit-Position: refs/heads/master@{#442938}

tools/clang/rewrite_to_chrome_style/RewriteToChromeStyle.cpp

@@ -449,8 +449,11 @@ bool CanBeEvaluatedAtCompileTime(const clang::Stmt* stmt,
     case clang::Stmt::DeclRefExprClass: {
       auto* declref = clang::dyn_cast<clang::DeclRefExpr>(expr);
       auto* decl = declref->getDecl();
-      if (clang::dyn_cast<clang::VarDecl>(decl))
+      if (auto* vardecl = clang::dyn_cast<clang::VarDecl>(decl)) {
+        if (auto* initializer = vardecl->getInit())
+          return CanBeEvaluatedAtCompileTime(initializer, context);
         return false;
+      }
       break;
     }
 

tools/clang/rewrite_to_chrome_style/tests/template-expected.cc

@@ -64,6 +64,8 @@ void F() {
   const bool kComplexConst = number || (number + 1);
   // A complex statement with a non-const thing is not const.
   const bool complex_not_const = number || (g_global_number + 1);
+  // A const built from other consts is a const.
+  const bool kConstFromAConst = kComplexConst || number;
 }
 
 template <int number, typename... T>

tools/clang/rewrite_to_chrome_style/tests/template-original.cc

@@ -63,6 +63,8 @@ void F() {
   const bool complexConst = number || (number + 1);
   // A complex statement with a non-const thing is not const.
   const bool complexNotConst = number || (g_globalNumber + 1);
+  // A const built from other consts is a const.
+  const bool constFromAConst = complexConst || number;
 }
 
 template <int number, typename... T>