Make IsSolidColor() a property on CC scrollbar layers.

cc/base/switches.cc

Index: cc/base/switches.cc
diff --git a/cc/base/switches.cc b/cc/base/switches.cc
index 77682e67d4380680f8a540a8282cc7f64e31483e..c1fc8ecf9fb18cf4ca34ae19cedcde998a11c1d7 100644
--- a/cc/base/switches.cc
+++ b/cc/base/switches.cc
@@ -134,6 +134,21 @@ const char kCCLayerTreeTestNoTimeout[] = "cc-layer-tree-test-no-timeout";
 const char kCCUnittestsTraceEventsToVLOG[] =
     "cc-unittests-trace-events-to-vlog";
 
+// Allow forcing of solid-color scrollbars
+const char kForceSolidColorScrollbars[] = "force-solid-color-scrollbars";
+
+// Solid-color scrollbar color in hex ARGB format, e.g. 0x80808080.
+// The 0x/0X prefix is optional.
+const char kSolidColorScrollbarColor[] = "solid-color-scrollbar-color";
+
+// Solid-color scrollbar thickness in DIP.
+const char kSolidColorScrollbarThickness[] = "solid-color-scrollbar-thickness";
+
+bool ForceSolidColorScrollbars() {
+  return CommandLine::ForCurrentProcess()->HasSwitch(
+      cc::switches::kForceSolidColorScrollbars);
+}
+
 bool IsImplSidePaintingEnabled() {
   const CommandLine& command_line = *CommandLine::ForCurrentProcess();