PDF Viewer: Delegate two-up-view tracking to the plugin

Currently, both the plugin and the UI track the state of two-up-view.
Additionally, the state tracked by the plugin is consistently sent to
the UI.

While two-up-view can only be invoked on through the UI, the feature
actually occurs asynchronously. It would be better to update the UI
state with that of the plugin.

Change-Id: Id0b40c2fa0d7d4eb029bbb06d8eb162871938385
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2631360
Commit-Queue: Daniel Hosseinian <dhoss@chromium.org>
Reviewed-by: dpapad <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844870}

chrome/browser/resources/pdf/pdf_viewer.js

@@ -544,7 +544,6 @@ export class PDFViewerElement extends PDFViewerBaseElement {
   onResetView_() {
     if (this.twoUpViewEnabled_) {
       this.currentController.setTwoUpView(false);
-      this.twoUpViewEnabled_ = false;
     }
 
     const rotations = this.viewport.getClockwiseRotations();
@@ -777,12 +776,12 @@ export class PDFViewerElement extends PDFViewerBaseElement {
    * @private
    */
   onTwoUpViewChanged_(e) {
-    this.twoUpViewEnabled_ = e.detail;
-    this.currentController.setTwoUpView(this.twoUpViewEnabled_);
+    const twoUpViewEnabled = e.detail;
+    this.currentController.setTwoUpView(twoUpViewEnabled);
     if (!this.pdfViewerUpdateEnabled_) {
       this.toolbarManager_.forceHideTopToolbar();
     }
-    recordTwoUpViewEnabled(this.twoUpViewEnabled_);
+    recordTwoUpViewEnabled(twoUpViewEnabled);
   }
 
   /**
@@ -848,12 +847,9 @@ export class PDFViewerElement extends PDFViewerBaseElement {
     }
 
     // Update toolbar elements.
-    if (this.toolbarEnabled_) {
-      const visiblePage = this.viewport.getMostVisiblePage();
-      this.pageNo_ = visiblePage + 1;
-
     this.clockwiseRotations_ = this.viewport.getClockwiseRotations();
-    }
+    this.pageNo_ = this.viewport.getMostVisiblePage() + 1;
+    this.twoUpViewEnabled_ = this.viewport.twoUpViewEnabled();
 
     this.currentController.viewportChanged();
   }

chrome/browser/resources/pdf/viewport.js

@@ -237,10 +237,7 @@ export class Viewport {
   /** @return {boolean} Whether viewport is in two-up view mode. */
   twoUpViewEnabled() {
     const options = this.getLayoutOptions();
-    if (options === undefined) {
-      return false;
-    }
-    return options.twoUpViewEnabled;
+    return !!options && options.twoUpViewEnabled;
   }
 
   /**