[iOS] Enable/disable TextZoom reset button based on reset state

Right now, only the zoom in/out buttons adjust based on whether zooming
in or out would change anything. The reset button should adjust the
same way.

Bug: 1053977
Change-Id: I83903b4a55953e4984a61f9ba6b7eaa8858d95fe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2063134
Commit-Queue: Robbie Gibson <rkgibson@google.com>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742652}

ios/chrome/browser/ui/text_zoom/text_zoom_consumer.h

@@ -11,6 +11,8 @@
 - (void)setZoomInEnabled:(BOOL)enabled;
 // Tells the consumer that the user can currently zoom out.
 - (void)setZoomOutEnabled:(BOOL)enabled;
+// Tells the consumer that the user can currently reset the zoom level.
+- (void)setResetZoomEnabled:(BOOL)enabled;
 
 @end
 

ios/chrome/browser/ui/text_zoom/text_zoom_mediator.mm

@@ -129,6 +129,8 @@
 - (void)updateConsumerState {
   [self.consumer setZoomInEnabled:self.fontSizeTabHelper->CanUserZoomIn()];
   [self.consumer setZoomOutEnabled:self.fontSizeTabHelper->CanUserZoomOut()];
+  [self.consumer
+      setResetZoomEnabled:self.fontSizeTabHelper->CanUserResetZoom()];
 }
 
 #pragma mark - CRWWebStateObserver

ios/chrome/browser/ui/text_zoom/text_zoom_view_controller.mm

@@ -208,4 +208,8 @@ const CGFloat kDividerWidth = 1;
   self.decrementButton.enabled = enabled;
 }
 
+- (void)setResetZoomEnabled:(BOOL)enabled {
+  self.resetButton.enabled = enabled;
+}
+
 @end

ios/chrome/browser/web/font_size_tab_helper.h

@@ -43,6 +43,9 @@ class FontSizeTabHelper : public web::WebStateObserver,
   // Returns whether the user can still zoom out. (I.e., They have not reached
   // the min zoom level.).
   bool CanUserZoomOut() const;
+  // Returns whether the user can reset the zoom level. (I.e., They are not at
+  // the default zoom level.)
+  bool CanUserResetZoom() const;
 
   // Remove any stored zoom levels from the provided |PrefService|.
   static void ClearUserZoomPrefs(PrefService* pref_service);

ios/chrome/browser/web/font_size_tab_helper.mm

@@ -192,6 +192,12 @@ bool FontSizeTabHelper::CanUserZoomOut() const {
   return NewMultiplierAfterZoom(ZOOM_OUT).has_value();
 }
 
+bool FontSizeTabHelper::CanUserResetZoom() const {
+  base::Optional<double> new_multiplier = NewMultiplierAfterZoom(ZOOM_RESET);
+  return new_multiplier.has_value() &&
+         new_multiplier.value() != GetCurrentUserZoomMultiplier();
+}
+
 int FontSizeTabHelper::GetFontSize() const {
   // Multiply by 100 as the web property needs a percentage.
   return SystemSuggestedFontSizeMultiplier() * GetCurrentUserZoomMultiplier() *