vaapi_wrapper: fix a few error messages

A failure of VADisplayState::Initialize() means that all hardware
acceleration features (not just decoding) will not be available. Fix the
newly added error messages to better reflect that.

Also replace the very generic "HW" with a more precise "VAAPI" to allow
the user to better understand the origin of the error.

BUG=None
TEST=None, this just improves error messages

Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I7ff94f0b4a72862c2838e7096e353a2d6e23ba87
Reviewed-on: https://chromium-review.googlesource.com/802611Reviewed-by: Wu-Cheng Li <wuchengli@chromium.org>
Commit-Queue: Alexandre Courbot <acourbot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#520902}

media/gpu/vaapi_wrapper.cc

@@ -248,7 +248,7 @@ bool VADisplayState::Initialize() {
 #if defined(USE_X11)
       va_display_ = vaGetDisplay(gfx::GetXDisplay());
 #else
-      LOG(WARNING) << "HW video decode acceleration not available without "
+      LOG(WARNING) << "VAAPI video acceleration not available without "
                       "DesktopGL (GLX).";
 #endif  // USE_X11
       break;
@@ -263,7 +263,7 @@ bool VADisplayState::Initialize() {
       break;
 
     default:
-      LOG(WARNING) << "HW video decode acceleration not available for "
+      LOG(WARNING) << "VAAPI video acceleration not available for "
                    << gl::GetGLImplementationName(gl::GetGLImplementation());
       return false;
   }