[ios] Add bold to favicon fallback monogram

Screenshot: https://drive.google.com/open?id=1HyMQ4s95UdTZVXdTqawSS4zIM8vDY_uF

Change-Id: I91a2a0e337cb4b43985f1307ff05abbddc3ed71f
Reviewed-on: https://chromium-review.googlesource.com/1133740Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Chris Lu <thegreenfrog@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575027}

ios/chrome/common/favicon/favicon_view.mm

@@ -40,8 +40,13 @@ const CGFloat kDefaultCornerRadius = 3;
 
     _faviconFallbackLabel = [[UILabel alloc] initWithFrame:self.bounds];
     _faviconFallbackLabel.textAlignment = NSTextAlignmentCenter;
+    UIFontDescriptor* baseDescriptor = [UIFontDescriptor
+        preferredFontDescriptorWithTextStyle:UIFontTextStyleCaption1];
+    UIFontDescriptor* styleDescriptor = [baseDescriptor
+        fontDescriptorWithSymbolicTraits:UIFontDescriptorTraitBold];
+    // Use a |size| of 0.0 to use the default size for the descriptor.
     _faviconFallbackLabel.font =
-        [UIFont preferredFontForTextStyle:UIFontTextStyleCaption1];
+        [UIFont fontWithDescriptor:styleDescriptor size:0.0];
     _faviconFallbackLabel.isAccessibilityElement = NO;
     _faviconFallbackLabel.clipsToBounds = YES;
     _faviconFallbackLabel.layer.cornerRadius = kDefaultCornerRadius;
@@ -85,6 +90,19 @@ const CGFloat kDefaultCornerRadius = 3;
   self.faviconFallbackLabel.font = font;
 }
 
+- (void)traitCollectionDidChange:(UITraitCollection*)pTC {
+  if (pTC.preferredContentSizeCategory !=
+      self.traitCollection.preferredContentSizeCategory) {
+    UIFontDescriptor* baseDescriptor = [UIFontDescriptor
+        preferredFontDescriptorWithTextStyle:UIFontTextStyleCaption1];
+    UIFontDescriptor* styleDescriptor = [baseDescriptor
+        fontDescriptorWithSymbolicTraits:UIFontDescriptorTraitBold];
+    // Use a |size| of 0.0 to use the default size for the descriptor.
+    _faviconFallbackLabel.font =
+        [UIFont fontWithDescriptor:styleDescriptor size:0.0];
+  }
+}
+
 #pragma mark - UIView
 
 - (CGSize)intrinsicContentSize {