Use the single char overload of append() when possible.

third_party/WebKit/Source/platform/v8_inspector/V8DebuggerAgentImpl.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "platform/v8_inspector/V8DebuggerAgentImpl.h"
 
 #include "platform/inspector_protocol/String16.h"
 #include "platform/inspector_protocol/Values.h"
 #include "platform/v8_inspector/InjectedScript.h"
 #include "platform/v8_inspector/InspectedContext.h"
@@ skipping 822 matching lines @@
 
 void V8DebuggerAgentImpl::setBlackboxPatterns(ErrorString* errorString, std::unique_ptr<protocol::Array<String16>> patterns)
 {
     if (!patterns->length()) {
         m_blackboxPattern = nullptr;
         m_state->remove(DebuggerAgentState::blackboxPattern);
         return;
     }
 
     String16Builder patternBuilder;
-    patternBuilder.append("(");
-    for (size_t i = 0; i < patterns->length() - 1; ++i)
-        patternBuilder.append(patterns->get(i) + "|");
-    patternBuilder.append(patterns->get(patterns->length() - 1) + ")");
+    patternBuilder.append('(');
+    for (size_t i = 0; i < patterns->length() - 1; ++i) {
+        patternBuilder.append(patterns->get(i));
+        patternBuilder.append("|");
+    }
+    patternBuilder.append(patterns->get(patterns->length() - 1));
+    patternBuilder.append(')');
     String16 pattern = patternBuilder.toString();
     if (!setBlackboxPattern(errorString, pattern))
         return;
     m_state->setString(DebuggerAgentState::blackboxPattern, pattern);
 }
 
 bool V8DebuggerAgentImpl::setBlackboxPattern(ErrorString* errorString, const String16& pattern)
 {
     std::unique_ptr<V8Regex> regex(new V8Regex(m_debugger, pattern, true /** caseSensitive */, false /** multiline */));
     if (!regex->isValid()) {
@@ skipping 357 matching lines @@
 {
     if (!enabled())
         return;
     m_scheduledDebuggerStep = NoStep;
     m_scripts.clear();
     m_blackboxedPositions.clear();
     m_breakpointIdToDebuggerBreakpointIds.clear();
 }
 
 } // namespace blink