PDFs viewed inside a <webview> should navigate the same as PDFs in tabs.

chrome/browser/resources/pdf/pdf.js

Index: chrome/browser/resources/pdf/pdf.js
diff --git a/chrome/browser/resources/pdf/pdf.js b/chrome/browser/resources/pdf/pdf.js
index c8753e14a6207dca698cd16144c70cb57dba82f9..4ea2bf1dde3c694cd2e98701b4ba674d92205fbb 100644
--- a/chrome/browser/resources/pdf/pdf.js
+++ b/chrome/browser/resources/pdf/pdf.js
@@ -41,13 +41,14 @@ function getFilenameFromURL(url) {
 
 /**
  * Called when navigation happens in the current tab.
+ * @param {int} tabId The id of the current tab; -1 if no current tab.
  * @param {string} url The url to be opened in the current tab.
  */
-function onNavigateInCurrentTab(url) {
-  // Prefer the tabs API because it can navigate from one file:// URL to
-  // another.
-  if (chrome.tabs)
-    chrome.tabs.update({url: url});
+function onNavigateInCurrentTab(tabId, url) {
+  // When the PDFviewer is not inside a <webview>, prefer the tabs API because
+  // it can navigate from one file:// URL to another.
+  if (chrome.tabs && tabId != -1)
+    chrome.tabs.update(tabId, {url: url});
   else
     window.location.href = url;
 }
@@ -247,12 +248,18 @@ function PDFViewer(browserApi) {
   document.addEventListener('keydown', this.handleKeyEvent_.bind(this));
   document.addEventListener('mousemove', this.handleMouseEvent_.bind(this));
 
+  var onNavigateBoundToCurrentTab = function(url) {
+    var tabId = this.browserApi_ ? this.browserApi.getStreamInfo().tabId : -1;
+    onNavigateInCurrentTab(tabId, url);
+  };
+
   // Parse open pdf parameters.
   this.paramsParser_ =
       new OpenPDFParamsParser(this.getNamedDestination_.bind(this));
   this.navigator_ = new Navigator(this.browserApi_.getStreamInfo().originalUrl,
                                   this.viewport_, this.paramsParser_,
-                                  onNavigateInCurrentTab, onNavigateInNewTab);
+                                  onNavigateBoundToCurrentTab,
+                                  onNavigateInNewTab);
   this.viewportScroller_ =
       new ViewportScroller(this.viewport_, this.plugin_, window);
 }