Add StringBuilder::erase(index)

third_party/WebKit/Source/platform/wtf/text/StringBuilder.cpp

Index: third_party/WebKit/Source/platform/wtf/text/StringBuilder.cpp
diff --git a/third_party/WebKit/Source/platform/wtf/text/StringBuilder.cpp b/third_party/WebKit/Source/platform/wtf/text/StringBuilder.cpp
index 0e112bea782c58d0821612e139e5dd6ceae1320b..91c3e5c172ca8feaa5e54b8a2c3955bec13dacec 100644
--- a/third_party/WebKit/Source/platform/wtf/text/StringBuilder.cpp
+++ b/third_party/WebKit/Source/platform/wtf/text/StringBuilder.cpp
@@ -230,4 +230,20 @@ void StringBuilder::AppendNumber(double number, unsigned precision) {
   Append(NumberToFixedPrecisionString(number, precision, buffer));
 }
 
+void StringBuilder::erase(unsigned index) {
+  if (index >= length_)
+    return;
+  if (index == length_ - 1)
+    return Resize(index);
+
+  if (is8_bit_) {
+    EnsureBuffer8(0);

[haraken, 2017/06/23 13:16:49]

Do you need this?

[kojii, 2017/06/23 13:45:23]

Yes, since StringBuilder may have StringImpl but not buffer yet. This ensures
there's a buffer, and StringImpl is copied into it.

I can call it only when "!HasBuffer()", but that's all what "EnsureBuffer" does;
it calls CreateBuffer() if !HasBuffer.

+    buffer8_->erase(index);
+  } else {
+    EnsureBuffer16(0);

[haraken, 2017/06/23 13:16:49]

Ditto.

+    buffer16_->erase(index);
+  }
+  --length_;

[haraken, 2017/06/23 13:16:49]

Do you want to call Resize() in this case as well?

It looks inconsistent that you call Resize() only when index == length_ - 1.

[kojii, 2017/06/23 13:45:23]

I guess you misunderstood something, probably due to micro-optimization I put
in? Resize() does two things:
1. Change buffer8_/buffer16_.
2. Change length_.
Since this function changes buffer8_/buffer16_, we can't call Resize() here.

The Resize() call, as mentioned above, is a suspective micro-optimization for
when removing the last character, I guess I shouldn't put it in if it makes
readability worse. Should I?

[haraken, 2017/06/23 13:56:17]

Makes sense. Yeah, remove it or add a comment.

[kojii, 2017/06/23 14:04:21]

Thank you for prompt reply, removed.

+}
+
 }  // namespace WTF