Links in PDF should open in a new window when shift + left clicked.

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 c7b172078d7778472af64c4fe851a35bca15b73e..8cb012aac9e48dbcdb594a64267c344fb5848585 100644
--- a/chrome/browser/resources/pdf/pdf.js
+++ b/chrome/browser/resources/pdf/pdf.js
@@ -70,6 +70,19 @@ function onNavigateInNewTab(url, active) {
 }
 
 /**
+ * Called when navigation happens in the new window.
+ * @param {string} url The url to be opened in the new window.
+ */
+function onNavigateInNewWindow(url) {
+  // Prefer the windows API because it guarantees we can just open a new window.
+  // window.open with '_blank' argument doesn't have this guarantee.
+  if (chrome.windows)
+    chrome.windows.create({url: url});
+  else
+    window.open(url, '_blank');
+}
+
+/**
  * Whether keydown events should currently be ignored. Events are ignored when
  * an editable element has focus, to allow for proper editing controls.
  * @param {HTMLElement} activeElement The currently selected DOM node.
@@ -265,7 +278,7 @@ function PDFViewer(browserApi) {
                                   onNavigateInCurrentTab.bind(undefined,
                                                               isInTab,
                                                               isSourceFileUrl),
-                                  onNavigateInNewTab);
+                                  onNavigateInNewTab, onNavigateInNewWindow);
   this.viewportScroller_ =
       new ViewportScroller(this.viewport_, this.plugin_, window);