Ensure pdf plugin sends DidStartLoading() consistently

There are situations where the pdf plugin will initialize itself in such a way
that it never notifies content/renderer/ that it has started. In so doing, it
also fails to send a stop message, since it tries to ensure it doesn't send
mismatched start/stop messages.

Print preview decides when to display the preview based on when loading
stops. Since this only considers the page's content and not the pdf plugin's
initialization, there is a race condition where we may try to preview before
the plugin is ready. In this cases, we show "Loading preivew..." and never load
the actual preview.

There is a hack in place in print_preview_web_helper.cc to delay the process of
showing the preview to maximize the chance that the pdf plugin will be ready.
This change should allow us to rip that out.

BUG=376969

Review URL: https://codereview.chromium.org/397713005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@283837 0039d316-1c4b-4281-b951-d872f2087c98

chrome/renderer/printing/print_web_view_helper.cc

@@ -1703,13 +1703,10 @@ void PrintWebViewHelper::RequestPrintPreview(PrintPreviewRequestType type) {
         // |is_modifiable| value until they are fully loaded, which occurs when
         // DidStopLoading() is called. Defer showing the preview until then.
       } else {
-        // TODO(japhet): This delay is a terrible hack. See crbug.com/376969
-        // for the motivation.
-        base::MessageLoop::current()->PostDelayedTask(
+        base::MessageLoop::current()->PostTask(
             FROM_HERE,
             base::Bind(&PrintWebViewHelper::ShowScriptedPrintPreview,
-                       weak_ptr_factory_.GetWeakPtr()),
-            base::TimeDelta::FromMilliseconds(100));
+                       weak_ptr_factory_.GetWeakPtr()));
       }
       IPC::SyncMessage* msg =
           new PrintHostMsg_SetupScriptedPrintPreview(routing_id());

pdf/instance.cc

@@ -349,6 +349,10 @@ bool Instance::Init(uint32_t argc, const char* argn[], const char* argv[]) {
     // For PDFs embedded in a frame, we don't get the data automatically like we
     // do for full-frame loads.  Start loading the data manually.
     LoadUrl(url);
+  } else {
+    DCHECK(!did_call_start_loading_);
+    pp::PDF::DidStartLoading(this);
+    did_call_start_loading_ = true;
   }
 
   ZoomLimitsChanged(kMinZoom, kMaxZoom);