Fixes document type detection on iOS 9.

ios/web/web_state/ui/crw_ui_web_view_web_controller.mm

Index: ios/web/web_state/ui/crw_ui_web_view_web_controller.mm
diff --git a/ios/web/web_state/ui/crw_ui_web_view_web_controller.mm b/ios/web/web_state/ui/crw_ui_web_view_web_controller.mm
index 8888ca50ed4dc63499cac7b99af2524868fb9742..9bc07e431b9b49e2378c5904ca0f659c30040ff4 100644
--- a/ios/web/web_state/ui/crw_ui_web_view_web_controller.mm
+++ b/ios/web/web_state/ui/crw_ui_web_view_web_controller.mm
@@ -4,6 +4,7 @@
 
 #import "ios/web/web_state/ui/crw_ui_web_view_web_controller.h"
 
+#import "base/ios/ios_util.h"
 #import "base/ios/ns_error_util.h"
 #import "base/ios/weak_nsobject.h"
 #include "base/json/json_reader.h"
@@ -550,13 +551,25 @@ const size_t kMaxMessageQueueSize = 262144;
   if (!_uiWebView) {
     return web::WEB_VIEW_DOCUMENT_TYPE_GENERIC;
   }
-  NSString* documentType =
-      [_uiWebView stringByEvaluatingJavaScriptFromString:
-          @"'' + document"];
-  if ([documentType isEqualToString:@"[object HTMLDocument]"])
-    return web::WEB_VIEW_DOCUMENT_TYPE_HTML;
-  else if ([documentType isEqualToString:@"[object Document]"])
-    return web::WEB_VIEW_DOCUMENT_TYPE_GENERIC;
+
+  if (base::ios::IsRunningOnIOS9OrLater()) {
+    // On iOS 9, evaluating '' + document always results in [object
+    // HTMLDocument], even for PDFs. However, document.contentType is properly
+    // defined.
+    NSString* MIMEType = [_uiWebView
+        stringByEvaluatingJavaScriptFromString:@"document.contentType"];
+    return [self documentTypeFromMIMEType:MIMEType];
+  } else {
+    // On iOS 8 and below, document.contentType is always undefined. Use this
+    // instead.
+    NSString* documentType =
+        [_uiWebView stringByEvaluatingJavaScriptFromString:@"'' + document"];
+    if ([documentType isEqualToString:@"[object HTMLDocument]"])
+      return web::WEB_VIEW_DOCUMENT_TYPE_HTML;
+    else if ([documentType isEqualToString:@"[object Document]"])
+      return web::WEB_VIEW_DOCUMENT_TYPE_GENERIC;
+  }
+
   return web::WEB_VIEW_DOCUMENT_TYPE_UNKNOWN;
 }