Changed two assertions to explicit tests, and added an error code to

src/libEGL/Display.cpp

@@ -297,8 +297,11 @@ void Display::startScene()
     if (!mSceneStarted)
     {
         long result = mDevice->BeginScene();
-        ASSERT(SUCCEEDED(result));
-        mSceneStarted = true;
+        if (SUCCEEDED(result)) {
+            // This is defensive checking against the device being
+            // lost at unexpected times.
+            mSceneStarted = true;
+        }
     }
 }
 
@@ -306,8 +309,9 @@ void Display::endScene()
 {
     if (mSceneStarted)
     {
-        long result = mDevice->EndScene();
-        ASSERT(SUCCEEDED(result));
+        // EndScene can fail if the device was lost, for example due
+        // to a TDR during a draw call.
+        mDevice->EndScene();
         mSceneStarted = false;
     }
 }

src/libGLESv2/Context.cpp

@@ -2158,8 +2158,11 @@ void Context::readPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum
 
         switch (result)
         {
+          // It turns out that D3D will sometimes produce more error
+          // codes than those documented.
           case D3DERR_DRIVERINTERNALERROR:
           case D3DERR_DEVICELOST:
+          case D3DERR_DEVICEHUNG:
             return error(GL_OUT_OF_MEMORY);
           default:
             UNREACHABLE();