Add EGL_ARM_implicit_external_sync extension support

ui/gl/gl_surface_ozone.cc

Index: ui/gl/gl_surface_ozone.cc
diff --git a/ui/gl/gl_surface_ozone.cc b/ui/gl/gl_surface_ozone.cc
index eecd06413876bdbceb9b0d7a50c26c5f40eb6559..ca88379d590d307a38f65107e41e4aff1a476035 100644
--- a/ui/gl/gl_surface_ozone.cc
+++ b/ui/gl/gl_surface_ozone.cc
@@ -105,7 +105,9 @@ class GL_EXPORT GLSurfaceOzoneSurfaceless : public SurfacelessEGL {
                             AcceleratedWidget widget)
       : SurfacelessEGL(gfx::Size()),
         ozone_surface_(ozone_surface.Pass()),
-        widget_(widget) {}
+        widget_(widget),
+        has_implicit_external_sync_(
+            HasEGLExtension("EGL_ARM_implicit_external_sync")) {}
 
   bool Initialize() override {
     if (!SurfacelessEGL::Initialize())
@@ -122,8 +124,8 @@ class GL_EXPORT GLSurfaceOzoneSurfaceless : public SurfacelessEGL {
     return SurfacelessEGL::Resize(size);
   }
   bool SwapBuffers() override {
-    // TODO: this should be replaced by a fence when supported by the driver.
-    glFlush();
+    if (!Flush())
+      return false;
     return ozone_surface_->OnSwapBuffers();
   }
   bool ScheduleOverlayPlane(int z_order,
@@ -143,8 +145,8 @@ class GL_EXPORT GLSurfaceOzoneSurfaceless : public SurfacelessEGL {
     return true;
   }
   bool SwapBuffersAsync(const SwapCompletionCallback& callback) override {
-    // TODO: this should be replaced by a fence when supported by the driver.
-    glFlush();
+    if (!Flush())
+      return false;
     return ozone_surface_->OnSwapBuffersAsync(callback);
   }
   bool PostSubBufferAsync(int x,
@@ -160,11 +162,33 @@ class GL_EXPORT GLSurfaceOzoneSurfaceless : public SurfacelessEGL {
     Destroy();  // EGL surface must be destroyed before SurfaceOzone
   }
 
+  bool Flush() {
+    glFlush();
+    // TODO: the following should be replaced by a per surface flush as it gets
+    // implemented in GL drivers.
+    if (has_implicit_external_sync_) {
+      const EGLint attrib_list[] = {
+          EGL_SYNC_CONDITION_KHR,
+          EGL_SYNC_PRIOR_COMMANDS_IMPLICIT_EXTERNAL_ARM,
+          EGL_NONE};
+      EGLSyncKHR fence =
+          eglCreateSyncKHR(GetDisplay(), EGL_SYNC_FENCE_KHR, attrib_list);
+      if (fence) {
+        eglClientWaitSyncKHR(GetDisplay(), fence,
+                             EGL_SYNC_FLUSH_COMMANDS_BIT_KHR, EGL_FOREVER_KHR);

[piman, 2015/02/07 01:13:17]

nit: if we're doing EGL_SYNC_FLUSH_COMMANDS_BIT_KHR, we don't need the glFlush
on l.166. Maybe we can change the logic as 
if (has_implicit_external_sync_) {
  // Do fence logic
} else {
  glFlush();
}

[piman, 2015/02/07 01:13:17]

As a potential optimization, should we delay the ClientWaitSync until we're
about to submit the flip? In case there's already a pending flip we will delay
scheduling this flip, so we could delay the ClientWaitSync for better overlap.
Maybe keep as a TODO / file a bug?

[dnicoara, 2015/02/07 02:03:36]

+1 for TODO and bug. I was talking to Alex about this a few weeks back. We were
discussing optimizing this so we wouldn't block the GPU main thread for this
operation.

+        eglDestroySyncKHR(GetDisplay(), fence);
+      } else {
+        return false;
+      }
+    }
+    return true;
+  }
+
   // The native surface. Deleting this is allowed to free the EGLNativeWindow.
   scoped_ptr<ui::SurfaceOzoneEGL> ozone_surface_;
   AcceleratedWidget widget_;
   scoped_ptr<VSyncProvider> vsync_provider_;
-
+  bool has_implicit_external_sync_;
   DISALLOW_COPY_AND_ASSIGN(GLSurfaceOzoneSurfaceless);
 };