[XProto] Fix GPU process crash when Xlib is not implicitly loaded

The old code used dlsym(RTLD_DEFAULT), which will attempt to obtain the
symbol from libraries already loaded.  This works most of the time
because Xlib gets loaded by eg. GTK, but in cases where Xlib is not
already loaded (eg. certain ChromeOS setups), XFree will not be found,
leading to a crash.  The fix is to switch to the existing xlib_support
which internally does dlopen("libX11.so.6") so it shouldn't have this
issue.

R=sky

Bug: 1150918
Change-Id: I82d28cf86e187cc1213b607482f7bd1f4a8e2287
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2552209
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Auto-Submit: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#829901}

ui/gfx/x/BUILD.gn

@@ -34,6 +34,7 @@ generate_library_loader("xlib_loader") {
     "XFlush",
     "XSynchronize",
     "XSetErrorHandler",
+    "XFree",
   ]
 }
 

ui/gfx/x/xlib.h

@@ -12,6 +12,7 @@ int XCloseDisplay(struct _XDisplay*);
 int XFlush(struct _XDisplay*);
 int XSynchronize(struct _XDisplay*, int);
 int XSetErrorHandler(int (*)(void*, void*));
+void XFree(void*);
 }
 
 #endif  // UI_GFX_X_XLIB_H_

ui/gfx/x/xlib_support.cc

@@ -49,6 +49,11 @@ void SetXlibErrorHandler() {
   GetXlibLoader()->XSetErrorHandler(XlibErrorHandler);
 }
 
+DISABLE_CFI_ICALL
+void XlibFree(void* data) {
+  GetXlibLoader()->XFree(data);
+}
+
 DISABLE_CFI_ICALL
 XlibDisplay::XlibDisplay(const std::string& address) {
   InitXlib();

ui/gfx/x/xlib_support.h

@@ -32,6 +32,9 @@ COMPONENT_EXPORT(X11) void InitXlib();
 // Sets an async error handler which only logs an error message.
 COMPONENT_EXPORT(X11) void SetXlibErrorHandler();
 
+// Wraps XFree().
+COMPONENT_EXPORT(X11) void XlibFree(void* data);
+
 // A scoped Xlib display.
 class COMPONENT_EXPORT(X11) XlibDisplay {
  public:

ui/gl/glx_util.cc

@@ -62,13 +62,6 @@ x11::Glx::FbConfig GetConfigForWindow(x11::Connection* conn,
   return {};
 }
 
-NO_SANITIZE("cfi-icall")
-void XlibFree(void* data) {
-  using xfree_type = void (*)(void*);
-  auto* xfree = reinterpret_cast<xfree_type>(dlsym(RTLD_DEFAULT, "XFree"));
-  xfree(data);
-}
-
 }  // namespace
 
 GLXFBConfig GetFbConfigForWindow(x11::Connection* connection,
@@ -89,7 +82,7 @@ GLXFBConfig GetGlxFbConfigForXProtoFbConfig(x11::Connection* connection,
   DCHECK_EQ(nitems, 1);
   DCHECK(glx_configs);
   GLXFBConfig glx_config = glx_configs[0];
-  XlibFree(glx_configs);
+  x11::XlibFree(glx_configs);
   return glx_config;
 }