Reapply r9870 "Remove some initialization checks based on source positions.".

src/parser.cc

Index: src/parser.cc
diff --git a/src/parser.cc b/src/parser.cc
index 3e85c7a6ab4e32fc2b0a178859a1eb42468e319c..c2177bb218a46cf3f6c79b54e85d2384d9fa007c 100644
--- a/src/parser.cc
+++ b/src/parser.cc
@@ -1773,7 +1773,7 @@ Block* Parser::ParseVariableDeclarations(
     // For let/const declarations in harmony mode, we can also immediately
     // pre-resolve the proxy because it resides in the same scope as the
     // declaration.
-    Declare(name, mode, NULL, mode != VAR, CHECK_OK);
+    VariableProxy* proxy = Declare(name, mode, NULL, mode != VAR, CHECK_OK);
     nvars++;
     if (declaration_scope->num_var_or_const() > kMaxNumFunctionLocals) {
       ReportMessageAt(scanner().location(), "too_many_variables",
@@ -1828,6 +1828,11 @@ Block* Parser::ParseVariableDeclarations(
       if (decl_props != NULL) *decl_props = kHasInitializers;
     }
 
+    // Record the end position of the initializer.
+    if (proxy->var() != NULL) {
+      proxy->var()->set_initializer_position(scanner().location().end_pos);
+    }
+
     // Make sure that 'const x' and 'let x' initialize 'x' to undefined.
     if (value == NULL && needs_init) {
       value = GetLiteralUndefined();