[builtins] Migrate String.prototype.trim/trimLeft/trimRight to C++.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index a47a45dcb4b01df9d29e384b9f1adff55a26e3b3..3eb5368e4f1d5b7ed61ee85a2e5e6f2bc0933022 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -9982,6 +9982,36 @@ bool DescriptorArray::IsEqualTo(DescriptorArray* other) {
 }
 #endif
 
+// static
+Handle<String> String::Trim(Handle<String> string, TrimMode mode) {
+  Isolate* const isolate = string->GetIsolate();
+
+  // Flatten the input {string}.

[Franzi, 2016/05/27 14:20:08]

Do we need this comment?

[Benedikt Meurer, 2016/05/27 17:20:58]

Done.

+  string = String::Flatten(string);
+  int const length = string->length();
+
+  // Perform left trimming if requested.
+  int left = 0;
+  UnicodeCache* unicode_cache = isolate->unicode_cache();
+  if (mode & kTrimLeft) {

[Franzi, 2016/05/27 14:20:08]

For readability, I would prefer

if (mode == kTrimLeft || mode == kTrim) {...}

Expecting a certain relationship between the values seems unnecessary to me.
Then we don't need the initializers in the enum declaration. 
enum TrimMode {
  kTrimLeft,
  kTrimRight,
  kTrim
};

[Benedikt Meurer, 2016/05/27 17:20:58]

Good suggestion, thanks. Did that.

+    while (left < length &&
+           unicode_cache->IsWhiteSpaceOrLineTerminator(string->Get(left))) {
+      left++;
+    }
+  }
+
+  // Perform right trimming if requested.
+  int right = length;
+  if (mode & kTrimRight) {
+    while (
+        right > left &&
+        unicode_cache->IsWhiteSpaceOrLineTerminator(string->Get(right - 1))) {
+      right--;
+    }
+  }
+
+  return isolate->factory()->NewSubString(string, left, right);
+}
 
 bool String::LooksValid() {
   if (!GetIsolate()->heap()->Contains(this)) return false;