Clean up GLX extension string getters

There was a mismatch between methods of retrieving GLX extensions in
Chrome, causing certain available/used extensions to not appear on
about::gpu. Additionally, there is an opportunity to cache the extension
string and save calls.

Bug: 1043761
Change-Id: I39bde9702daf9b5cf80a5cc1c9a030ef56623913
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2015644
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735924}

ui/gl/gl_bindings.cc

@@ -77,7 +77,9 @@ std::string DriverEGL::GetClientExtensions() {
 
 #if defined(USE_GLX)
 std::string DriverGLX::GetPlatformExtensions() {
-  const char* str = glXQueryExtensionsString(gfx::GetXDisplay(), 0);
+  Display* display = gfx::GetXDisplay();
+  const int screen = (display == EGL_NO_DISPLAY ? 0 : DefaultScreen(display));
+  const char* str = glXQueryExtensionsString(display, screen);
   return str ? std::string(str) : "";
 }
 #endif

ui/gl/gl_glx_api_implementation.cc

@@ -79,7 +79,6 @@ const char* RealGLXApi::glXQueryExtensionsStringFn(Display* dpy,
 
   if (!driver_->fn.glXQueryExtensionsStringFn)
     return nullptr;
-
   const char* str = GLXApiBase::glXQueryExtensionsStringFn(dpy, screen);
   if (!str)
     return nullptr;
@@ -111,13 +110,10 @@ void TraceGLXApi::SetDisabledExtensions(
 bool GetGLWindowSystemBindingInfoGLX(const GLVersionInfo& gl_info,
                                      GLWindowSystemBindingInfo* info) {
   Display* display = glXGetCurrentDisplay();
-  const int kDefaultScreen = 0;
-  const char* vendor =
-      glXQueryServerString(display, kDefaultScreen, GLX_VENDOR);
-  const char* version =
-      glXQueryServerString(display, kDefaultScreen, GLX_VERSION);
-  const char* extensions =
-      glXQueryServerString(display, kDefaultScreen, GLX_EXTENSIONS);
+  const int screen = (display ? DefaultScreen(display) : 0);
+  const char* vendor = glXQueryServerString(display, screen, GLX_VENDOR);
+  const char* version = glXQueryServerString(display, screen, GLX_VERSION);
+  const char* extensions = glXQueryExtensionsString(display, screen);
   *info = GLWindowSystemBindingInfo();
   if (vendor)
     info->vendor = vendor;

ui/gl/gl_surface_glx.cc

@@ -12,6 +12,7 @@
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
+#include "base/no_destructor.h"
 #include "base/single_thread_task_runner.h"
 #include "base/synchronization/atomic_flag.h"
 #include "base/synchronization/lock.h"
@@ -532,9 +533,24 @@ void GLSurfaceGLX::ShutdownOneOff() {
   g_colormap = CopyFromParent;
 }
 
+// static
+std::string GLSurfaceGLX::QueryGLXExtensions() {
+  Display* display = gfx::GetXDisplay();
+  const int screen = (display ? DefaultScreen(display) : 0);
+  const char* extensions = glXQueryExtensionsString(display, screen);
+  if (extensions) {
+    return std::string(extensions);
+  }
+  return "";
+}
+
 // static
 const char* GLSurfaceGLX::GetGLXExtensions() {
-  return glXQueryExtensionsString(gfx::GetXDisplay(), 0);
+  static base::NoDestructor<std::string> glx_extensions("");
+  if (glx_extensions->empty()) {
+    *glx_extensions = QueryGLXExtensions();
+  }
+  return glx_extensions->c_str();
 }
 
 // static

ui/gl/gl_surface_glx.h

@@ -38,6 +38,7 @@ class GL_EXPORT GLSurfaceGLX : public GLSurface {
   // These aren't particularly tied to surfaces, but since we already
   // have the static InitializeOneOff here, it's easiest to reuse its
   // initialization guards.
+  static std::string QueryGLXExtensions();
   static const char* GetGLXExtensions();
   static bool HasGLXExtension(const char* name);
   static bool IsCreateContextSupported();