[DevTools] Migrate v8_inspector/public from String16 to String{View,Buffer}.

Using StringView for inbound parameters and StringBuffer for outbound helps to avoid copies in important places (mostly when passing large protocol messages around).

This opens possibility to:
- use WTF::String in core/inspector instead of String16;
- make String16 an alias to std::basic_string<uint16_t> to leverage all existing
optimizations.

One possible optimization is to migrate search utility (in V8StringUtil) to
StringView and avoid any copies of content there.

BUG=637032

Review-Url: https://codereview.chromium.org/2260233002
Cr-Original-Commit-Position: refs/heads/master@{#414846}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 101f402f95f5a67df948347edc4dce050ce482c7
7 files changed