OOP PDF: Do not call setZoom in response to an onZoomChange event.

chrome/browser/resources/pdf/zoom_manager.js

Index: chrome/browser/resources/pdf/zoom_manager.js
diff --git a/chrome/browser/resources/pdf/zoom_manager.js b/chrome/browser/resources/pdf/zoom_manager.js
new file mode 100644
index 0000000000000000000000000000000000000000..664c88fd41a0f17b1673332e2facb220033a9b73
--- /dev/null
+++ b/chrome/browser/resources/pdf/zoom_manager.js
@@ -0,0 +1,83 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+'use strict';
+
+/**
+ * A class that manages updating the browser with zoom changes.
+ */
+class ZoomManager {
+  /**
+   * Constructs a ZoomManager
+   * @param {!Viewport} viewport A Viewport for which to manage zoom.
+   * @param {Function} setBrowserZoomFunction A function that sets the browser
+   *     zoom to the provided value.
+   */
+  constructor(viewport, setBrowserZoomFunction) {
+    this.viewport_ = viewport;
+    this.setBrowserZoomFunction_ = setBrowserZoomFunction;
+    this.browserZoom_ = 1;
+    this.changingBrowserZoom_ = null;
+    this.onPdfZoomChange();
+  }
+
+  /**
+   * Invoked when a browser-initiated zoom-level change occurs.
+   * @param {number} newZoom the zoom level to zoom to.
+   */
+  onBrowserZoomChange(newZoom) {
+    // If we are changing the browser zoom level, ignore any browser zoom level
+    // change events. Either, the change occurred before our update and will be
+    // overwritten, or the change being reported is the change we are making,
+    // which we have already handled.
+    if (this.changingBrowserZoom_)
+      return;
+
+    if (this.floatingPointEquals(this.browserZoom_, newZoom))
+      return;
+
+    this.browserZoom_ = newZoom;
+    this.viewport_.setZoom(newZoom);
+  }
+
+  /**
+   * Invoked when an extension-initiated zoom-level change occurs.
+   */
+  onPdfZoomChange() {
+    // If we are already changing the browser zoom level in response to a
+    // previous extension-initiated zoom-level change, ignore this zoom change.
+    // Once the browser zoom level is changed, we check whether the extension's
+    // zoom level matches the most recently sent zoom level.
+    if (this.changingBrowserZoom_)
+      return;
+
+    let zoom = this.viewport_.zoom;
+    if (this.floatingPointEquals(this.browserZoom_, zoom))
+      return;
+
+    this.changingBrowserZoom_ = this.setBrowserZoomFunction_(zoom).then(
+        function() {
+      this.browserZoom_ = zoom;
+      this.changingBrowserZoom_ = null;
+
+      // The extension's zoom level may have changed while the browser zoom
+      // change was in progress. We call back into onPdfZoomChange to ensure the
+      // browser zoom is up to date.
+      this.onPdfZoomChange();
+    }.bind(this));
+  }
+
+  /**
+   * Returns whether two numbers are approximately equal.
+   * @param {number} a The first number.
+   * @param {number} b The second number.
+   */
+  floatingPointEquals(a, b) {
+    let MIN_ZOOM_DELTA = 0.01;
+    // If the zoom level is close enough to the current zoom level, don't
+    // change it. This avoids us getting into an infinite loop of zoom changes
+    // due to floating point error.
+    return Math.abs(a - b) <= MIN_ZOOM_DELTA;
+  }
+};