MacViews: Enable RenderTextHarfBuzz to get Textfields to work.

Textfields require RenderTextHarfBuzz to work properly on the Mac because
RenderTextMac's implementation is not complete.
But RenderTextMac is used by the Cocoa UI to perform string sizing and elliding,
HarfBuzz will not give the same answers.
So for now we turn on HarfBuzz conditionally on OS_MACOSX and TOOLKIT_VIEWS.
TextFieldModel and StyledLabel unit tests now pass without failures.

BUG=378134

Review URL: https://codereview.chromium.org/326093004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@276341 0039d316-1c4b-4281-b951-d872f2087c98

ui/gfx/render_text.cc

@@ -412,11 +412,16 @@ RenderText::~RenderText() {
 }
 
 RenderText* RenderText::CreateInstance() {
+#if defined(OS_MACOSX) && defined(TOOLKIT_VIEWS)
+  // Use the more complete HarfBuzz implementation for Views controls on Mac.
+  return new RenderTextHarfBuzz;
+#else
   if (CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kEnableHarfBuzzRenderText)) {
     return new RenderTextHarfBuzz;
   }
   return CreateNativeInstance();
+#endif
 }
 
 void RenderText::SetText(const base::string16& text) {