Avoid "using namespace blink" in global scope

With jumbo (unity builds, merged translation units) a "using blink"
statement intended for just the local translation unit will affect
many other translation units which causes various issues.

There is also (with jumbo) a warning about such usage that will prevent
things from compiling.

Without this patch this file will have to be manually excluded from
jumbo builds and I am trying to avoid such exclusion lists for
performance and maintenance.

Review-Url: https://codereview.chromium.org/2965323002
Cr-Commit-Position: refs/heads/master@{#487501}

third_party/WebKit/Source/core/editing/BUILD.gn

@@ -287,13 +287,6 @@ blink_core_sources("editing") {
     sources += [ "commands/SmartReplaceCF.cpp" ]
   }
 
-  if (is_mac) {
-    jumbo_excluded_sources = [
-      # Using "using blink" in global scope.
-      "WebSubstringUtil.mm",
-    ]
-  }
-
   configs += [
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     "//build/config/compiler:no_size_t_to_int_warning",

third_party/WebKit/Source/core/editing/WebSubstringUtil.mm

@@ -58,11 +58,12 @@
 #include "public/web/WebHitTestResult.h"
 #include "public/web/WebLocalFrame.h"
 
-using namespace blink;
+namespace blink {
+
+namespace {
 
-static NSAttributedString* attributedSubstringFromRange(
-    const EphemeralRange& range,
-    float fontScale) {
+NSAttributedString* attributedSubstringFromRange(const EphemeralRange& range,
+                                                 float fontScale) {
   NSMutableAttributedString* string = [[NSMutableAttributedString alloc] init];
   NSMutableDictionary* attrs = [NSMutableDictionary dictionary];
   size_t length = range.EndPosition().ComputeOffsetInContainerNode() -
@@ -149,7 +150,7 @@ WebPoint getBaselinePoint(LocalFrameView* frameView,
   return stringPoint;
 }
 
-namespace blink {
+}  // namespace
 
 NSAttributedString* WebSubstringUtil::AttributedWordAtPoint(
     WebFrameWidget* frame_widget,