Revert "Fix default font used in VR text element"

This reverts commit b5385fa9.

Reason for revert: Appears to have broken VR render tests https://crbug.com/1013009

Original change's description:
> Fix default font used in VR text element
> 
> The VR code is using the default font "sans-serif".
> The Font (and FontList) on that platform is the PlatformFontSkia
> When creating the font with the literal "sans-serif", there is
> not matched typeface.
> 
> The function creating the typeface has a fallback path that try
> "sans" which is the resulting typeface used.
> 
> see: https://cs.chromium.org/chromium/src/ui/gfx/platform_font_skia.cc?l=53
> 
> This CL avoid to use that fallback logic. Instead, we rely on
> the FontList behavior to use the default system font with the default
> constructor.
> 
> 
> R=​alcooper@chromium.org
> 
> Change-Id: I612502f32d77787b8f0346c0fc23cd65b68e3013
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1847902
> Reviewed-by: Klaus Weidner <klausw@chromium.org>
> Commit-Queue: Etienne Bergeron <etienneb@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#704279}

TBR=klausw@chromium.org,etienneb@chromium.org,alcooper@chromium.org

Change-Id: I7a54e9bf314a67661e625cbb4d838eea73560b75
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1852424Reviewed-by: Juan Antonio Navarro Pérez <perezju@chromium.org>
Commit-Queue: Juan Antonio Navarro Pérez <perezju@chromium.org>
Cr-Commit-Position: refs/heads/master@{#704530}

chrome/browser/vr/elements/text.cc

@@ -24,6 +24,7 @@ namespace {
 constexpr float kCursorWidthRatio = 0.07f;
 constexpr int kTextPixelPerDmm = 1100;
 constexpr float kTextShadowScaleFactor = 1000.0f;
+constexpr char kDefaultFontFamily[] = "sans-serif";
 
 int DmmToPixel(float dmm) {
   return static_cast<int>(dmm * kTextPixelPerDmm);
@@ -388,9 +389,8 @@ gfx::Size TextTexture::LayOutText() {
     text_bounds.set_width(DmmToPixel(text_width_));
   }
 
-  gfx::FontList fonts;
-  if (fonts.GetFontSize() != pixel_font_height)
-    fonts = fonts.DeriveWithSizeDelta(pixel_font_height - fonts.GetFontSize());
+  gfx::FontList fonts =
+      gfx::FontList(gfx::Font(kDefaultFontFamily, pixel_font_height));
 
   TextRenderParameters parameters;
   parameters.color = color_;