Fix gn build.

TBR=ishell@chromium.org

Review URL: https://codereview.chromium.org/723463002

Cr-Commit-Position: refs/heads/master@{#25277}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25277 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

BUILD.gn

@@ -896,8 +896,8 @@ source_set("v8_base") {
     "src/snapshot-source-sink.cc",
     "src/snapshot-source-sink.h",
     "src/snapshot.h",
+    "src/string-builder.cc",
     "src/string-builder.h",
-    "src/string-builder.c",
     "src/string-search.cc",
     "src/string-search.h",
     "src/string-stream.cc",

tools/gyp/v8.gyp

@@ -809,8 +809,8 @@
         '../../src/snapshot.h',
         '../../src/snapshot-source-sink.cc',
         '../../src/snapshot-source-sink.h',
-        '../../src/string-builder.h',
         '../../src/string-builder.cc',
+        '../../src/string-builder.h',
         '../../src/string-search.cc',
         '../../src/string-search.h',
         '../../src/string-stream.cc',