Reland 2: mac: Use a placeholder string for the family name of the system font.

Source/core/layout/LayoutTextControlMultiLine.cpp

Index: Source/core/layout/LayoutTextControlMultiLine.cpp
diff --git a/Source/core/layout/LayoutTextControlMultiLine.cpp b/Source/core/layout/LayoutTextControlMultiLine.cpp
index 6a67ae7fad0722e19b98b330ec44dd9dfd7ae5bd..132520816dc57125275d14ef46fc759b19b3811b 100644
--- a/Source/core/layout/LayoutTextControlMultiLine.cpp
+++ b/Source/core/layout/LayoutTextControlMultiLine.cpp
@@ -25,6 +25,10 @@
 #include "core/html/HTMLTextAreaElement.h"
 #include "core/layout/HitTestResult.h"
 
+#if defined(WTF_OS_MACOSX)
+#include "platform/mac/VersionUtilMac.h"
+#endif // defined(WTF_OS_MACOSX)
+
 namespace blink {
 
 LayoutTextControlMultiLine::LayoutTextControlMultiLine(HTMLTextAreaElement* element)
@@ -50,11 +54,16 @@ bool LayoutTextControlMultiLine::nodeAtPoint(HitTestResult& result, const HitTes
 
 float LayoutTextControlMultiLine::getAvgCharWidth(const AtomicString& family) const
 {
-    // Since Lucida Grande is the default font, we want this to match the width
-    // of Courier New, the default font for textareas in IE, Firefox and Safari Win.
-    // 1229 is the avgCharWidth value in the OS/2 table for Courier New.
-    if (family == "Lucida Grande")
+// Match the default system font to the width of MS Shell Dlg, the default
+// font for textareas in Firefox, Safari Win and IE for some encodings (in
+// IE, the default font is encoding specific). 1229 is the avgCharWidth
+// value in the OS/2 table for Courier New.
+// This is a hack which Blink no longer applies on OSX 10.10+.
+// https://code.google.com/p/chromium/issues/detail?id=515989#c8
+#if defined(WTF_OS_MACOSX)

[tkent, 2015/08/11 01:34:36]

We'd like to minimize OS-specific code in core/.  Please add new function to
LayoutTheme like LayoutTheme::needsSystemFontHackForTextControl(), implement it
in LayoutThemeMac.

[erikchen, 2015/08/11 05:21:13]

Done. I made a method called needsHackForTextControlWithFontFamily() which also
does the string comparison.

+    if (family == "BlinkMacSystemFont" && IsOSMavericksOrEarlier())
         return scaleEmToUnits(1229);
+#endif // defined(WTF_OS_MACOSX)
 
     return LayoutTextControl::getAvgCharWidth(family);
 }