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

Source/core/layout/LayoutTextControlSingleLine.cpp

Index: Source/core/layout/LayoutTextControlSingleLine.cpp
diff --git a/Source/core/layout/LayoutTextControlSingleLine.cpp b/Source/core/layout/LayoutTextControlSingleLine.cpp
index bf8ec2b730dad4147596d39d95d85dae3816184b..fd04ad6c0a2fe661631df2f11dffab5d0665bf03 100644
--- a/Source/core/layout/LayoutTextControlSingleLine.cpp
+++ b/Source/core/layout/LayoutTextControlSingleLine.cpp
@@ -40,6 +40,10 @@
 #include "platform/PlatformKeyboardEvent.h"
 #include "platform/fonts/SimpleFontData.h"
 
+#if defined(WTF_OS_MACOSX)
+#include "platform/mac/VersionUtilMac.h"
+#endif // defined(WTF_OS_MACOSX)
+
 namespace blink {
 
 using namespace HTMLNames;
@@ -299,12 +303,16 @@ LayoutRect LayoutTextControlSingleLine::controlClipRect(const LayoutPoint& addit
 
 float LayoutTextControlSingleLine::getAvgCharWidth(const AtomicString& family) const
 {
-    // Since Lucida Grande is the default font, we want this to match 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).
-    // 901 is the avgCharWidth value in the OS/2 table for MS Shell Dlg.
-    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). 901 is the avgCharWidth value
+// in the OS/2 table for MS Shell Dlg.
+// 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)
+    if (family == "BlinkMacSystemFont" && IsOSMavericksOrEarlier())
         return scaleEmToUnits(901);
+#endif // defined(WTF_OS_MACOSX)
 
     return LayoutTextControl::getAvgCharWidth(family);
 }
@@ -320,14 +328,21 @@ LayoutUnit LayoutTextControlSingleLine::preferredContentLogicalWidth(float charW
 
     float maxCharWidth = 0.f;
     AtomicString family = styleRef().font().fontDescription().family().family();
-    // Since Lucida Grande is the default font, we want this to match 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).
-    // 4027 is the (xMax - xMin) value in the "head" font table for MS Shell Dlg.
-    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). 4027 is the (xMax - xMin)
+// value in the "head" font table for MS Shell Dlg.
+// 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)
+    if (family == "BlinkMacSystemFont" && IsOSMavericksOrEarlier()) {
         maxCharWidth = scaleEmToUnits(4027);
-    else if (hasValidAvgCharWidth(family))
+    } else if (hasValidAvgCharWidth(family)) {
+#else
+    if (hasValidAvgCharWidth(family)) {
+#endif // defined(WTF_OS_MACOSX)
         maxCharWidth = roundf(styleRef().font().primaryFont()->maxCharWidth());
+    }
 
     // For text inputs, IE adds some extra width.
     if (maxCharWidth > 0.f)