media/gpu/v4l2: make accelerators work without GL

VideoDecodeAccelerators are supposed to work without GL support,
provided the make_context_current_cb_ callback is null. However the
Initialize() method of V4L2 accelerators checked for a valid EGL display
unconditionally. Move this check under the condition that
make_context_current_cb_ is not null, so that the V4L2 accelerators can
be used without an EGL display.

BUG=819542
TEST=Made sure VDA tests were still passing on eve, hana and kevin.

Change-Id: I632e85bad6871910c8a9114c6c34338c37262c08
Reviewed-on: https://chromium-review.googlesource.com/954767Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Dan Sanders <sandersd@chromium.org>
Commit-Queue: Alexandre Courbot <acourbot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542982}

media/gpu/v4l2/v4l2_slice_video_decode_accelerator.cc

@@ -549,13 +549,13 @@ bool V4L2SliceVideoDecodeAccelerator::Initialize(const Config& config,
     decode_client_ = client_;
   }
 
-  if (egl_display_ == EGL_NO_DISPLAY) {
-    VLOGF(1) << "could not get EGLDisplay";
-    return false;
-  }
-
   // We need the context to be initialized to query extensions.
   if (!make_context_current_cb_.is_null()) {
+    if (egl_display_ == EGL_NO_DISPLAY) {
+      VLOGF(1) << "could not get EGLDisplay";
+      return false;
+    }
+
     if (!make_context_current_cb_.Run()) {
       VLOGF(1) << "could not make context current";
       return false;

media/gpu/v4l2/v4l2_video_decode_accelerator.cc

@@ -222,13 +222,13 @@ bool V4L2VideoDecodeAccelerator::Initialize(const Config& config,
 
   video_profile_ = config.profile;
 
-  if (egl_display_ == EGL_NO_DISPLAY) {
-    VLOGF(1) << "could not get EGLDisplay";
-    return false;
-  }
-
   // We need the context to be initialized to query extensions.
   if (!make_context_current_cb_.is_null()) {
+    if (egl_display_ == EGL_NO_DISPLAY) {
+      VLOGF(1) << "could not get EGLDisplay";
+      return false;
+    }
+
     if (!make_context_current_cb_.Run()) {
       VLOGF(1) << "could not make context current";
       return false;