Address compilation warnings for android build.

src/parsing/scanner.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Features shared by parsing and pre-parsing scanners.
 
 #ifndef V8_PARSING_SCANNER_H_
 #define V8_PARSING_SCANNER_H_
 
 #include "src/allocation.h"
@@ skipping 144 matching lines @@
 
 class LiteralBuffer {
  public:
   LiteralBuffer() : is_one_byte_(true), position_(0), backing_store_() { }
 
   ~LiteralBuffer() { backing_store_.Dispose(); }
 
   INLINE(void AddChar(char code_unit)) {
     if (position_ >= backing_store_.length()) ExpandBuffer();
     DCHECK(is_one_byte_);
-    DCHECK(0 <= code_unit && code_unit <= kMaxAscii);
+    DCHECK(IsValidAscii(code_unit));
     backing_store_[position_] = static_cast<byte>(code_unit);
     position_ += kOneByteSize;
     return;
   }
 
   INLINE(void AddChar(uc32 code_unit)) {
     if (position_ >= backing_store_.length()) ExpandBuffer();
     if (is_one_byte_) {
       if (code_unit <= unibrow::Latin1::kMaxChar) {
         backing_store_[position_] = static_cast<byte>(code_unit);
@@ skipping 68 matching lines @@
         backing_store_ = other->backing_store_.Clone();
       }
     }
   }
 
  private:
   static const int kInitialCapacity = 16;
   static const int kGrowthFactory = 4;
   static const int kMinConversionSlack = 256;
   static const int kMaxGrowth = 1 * MB;
+
+  inline bool IsValidAscii(char code_unit) {
+    // Control characters and printable characters span the range of
+    // valid ASCII characters (0-127). Chars are unsigned on some
+    // platforms which causes compiler warnings if the validity check
+    // tests the lower bound >= 0 as it's always true.
+    return iscntrl(code_unit) || isprint(code_unit);
+  }
+
   inline int NewCapacity(int min_capacity) {
     int capacity = Max(min_capacity, backing_store_.length());
     int new_capacity = Min(capacity * kGrowthFactory, capacity + kMaxGrowth);
     return new_capacity;
   }
 
   void ExpandBuffer() {
     Vector<byte> new_store = Vector<byte>::New(NewCapacity(kInitialCapacity));
     MemCopy(new_store.start(), backing_store_.start(), position_);
     backing_store_.Dispose();
@@ skipping 558 matching lines @@
   bool allow_harmony_exponentiation_operator_;
 
   MessageTemplate::Template scanner_error_;
   Location scanner_error_location_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PARSING_SCANNER_H_