Fix signed / unsigned warnings for ?: operators reported by Xcode 4.x clang compiler.

The patch is based on the report provided by github user Zakay.

BUG=none
TEST=none

Review URL: https://chromiumcodereview.appspot.com/9592030

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10970 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/api.cc

@@ -525,7 +525,8 @@ Extension::Extension(const char* name,
                      int source_length)
     : name_(name),
       source_length_(source_length >= 0 ?
-                  source_length : (source ? strlen(source) : 0)),
+                     source_length :
+                     (source ? static_cast<int>(strlen(source)) : 0)),
       source_(source, source_length_),
       dep_count_(dep_count),
       deps_(deps),

src/hydrogen-instructions.cc

@@ -1348,12 +1348,13 @@ void HBinaryOperation::PrintDataTo(StringStream* stream) {
 
 Range* HBitwise::InferRange(Zone* zone) {
   if (op() == Token::BIT_XOR) return HValue::InferRange(zone);
+  const int32_t kDefaultMask = static_cast<int32_t>(0xffffffff);
   int32_t left_mask = (left()->range() != NULL)
       ? left()->range()->Mask()
-      : 0xffffffff;
+      : kDefaultMask;
   int32_t right_mask = (right()->range() != NULL)
       ? right()->range()->Mask()
-      : 0xffffffff;
+      : kDefaultMask;
   int32_t result_mask = (op() == Token::BIT_AND)
       ? left_mask & right_mask
       : left_mask | right_mask;