Have PlatformFontLinux Fallback to default

It is possible to font loading to fail. Such as when the peer closes during a
synchronous mojo call to load a font.

Currently this is treated as a fatal error, which leads to flaky tests.

This change updates PlatformFontLinux to instead fallback to providing the
default font in these cases. While logging the error.

TEST=mash_browser_tests

Bug: 738441
Change-Id: I2717a0fdf561be82e6d393863a0cfd13b19ae480
Reviewed-on: https://chromium-review.googlesource.com/568789Reviewed-by: Dan Erat <derat@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Jonathan Ross <jonross@chromium.org>
Cr-Commit-Position: refs/heads/master@{#486533}

ui/gfx/platform_font_linux.cc

@@ -171,8 +171,11 @@ Font PlatformFontLinux::DeriveFont(int size_delta,
       (weight == weight_ && style == style_)
           ? typeface_
           : CreateSkTypeface(style, weight, &new_family, &success);
-  CHECK(success) << "Could not find any font: " << new_family << ", "
-                 << kFallbackFontFamilyName;
+  if (!success) {
+    LOG(ERROR) << "Could not find any font: " << new_family << ", "
+               << kFallbackFontFamilyName << ". Falling back to the default";
+    return Font(new PlatformFontLinux);
+  }
 
   FontRenderParamsQuery query;
   query.families.push_back(new_family);
@@ -269,8 +272,14 @@ void PlatformFontLinux::InitFromDetails(
   typeface_ = typeface ? std::move(typeface)
                        : CreateSkTypeface(style & Font::ITALIC, weight,
                                           &font_family_, &success);
-  CHECK(success) << "Could not find any font: " << font_family_ << ", "
-                 << kFallbackFontFamilyName;
+
+  if (!success) {
+    LOG(ERROR) << "Could not find any font: " << font_family << ", "
+               << kFallbackFontFamilyName << ". Falling back to the default";
+
+    InitFromPlatformFont(g_default_font.Get().get());
+    return;
+  }
 
   font_size_pixels_ = font_size_pixels;
   style_ = style;