Add escape hatch for plugins in NavigationClient::CommitNavigation().

The current browser-side navigation code can ask the renderer to commit
a MIME type that it cannot handle. When this happens, the renderer
simply ignores the commit request, tripping the CHECKs added in
https://crrev.com/796508.

For now, allow these commits to silently fail and not commit a new
document...

Bug: 999255, 1115912, 1117282
Change-Id: I435831058db8e059b0389a8e2262f6bd72e875fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2360602
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799385}

content/renderer/render_frame_impl.cc

@@ -4267,6 +4267,11 @@ void RenderFrameImpl::DidCreateDocumentLoader(
   }
 }
 
+void RenderFrameImpl::WillFailCommitNavigation(CommitFailureReason) {
+  CHECK_EQ(NavigationCommitState::kWillCommit, navigation_commit_state_);
+  navigation_commit_state_ = NavigationCommitState::kDidCommit;
+}
+
 void RenderFrameImpl::DidCommitNavigation(
     const blink::WebHistoryItem& item,
     blink::WebHistoryCommitType commit_type,

content/renderer/render_frame_impl.h

@@ -678,6 +678,7 @@ class CONTENT_EXPORT RenderFrameImpl
   void WillSendSubmitEvent(const blink::WebFormElement& form) override;
   void DidCreateDocumentLoader(
       blink::WebDocumentLoader* document_loader) override;
+  void WillFailCommitNavigation(CommitFailureReason) override;
   void DidCommitNavigation(const blink::WebHistoryItem& item,
                            blink::WebHistoryCommitType commit_type,
                            bool should_reset_browser_interface_broker) override;

third_party/blink/public/web/web_local_frame_client.h

@@ -317,6 +317,15 @@ class BLINK_EXPORT WebLocalFrameClient {
   // datasource will become the provisional datasource for the frame.
   virtual void DidCreateDocumentLoader(WebDocumentLoader*) {}
 
+  // Used to inform the embedder that `WebNavigationControl::CommitNavigation`
+  // call will fail to commit a new document.
+  //
+  // TODO(https://crbug.com/1117282): Remove the need for these exceptions.
+  enum class CommitFailureReason {
+    kNoPluginForMimeType,
+  };
+  virtual void WillFailCommitNavigation(CommitFailureReason) {}
+
   // The navigation has been committed, as a result of
   // WebNavigationControl::CommitNavigation call. The newly created document
   // is committed to the frame, the encoding of the response body is known,

third_party/blink/renderer/core/loader/frame_loader.cc

@@ -78,6 +78,7 @@
 #include "third_party/blink/renderer/core/frame/local_frame_view.h"
 #include "third_party/blink/renderer/core/frame/settings.h"
 #include "third_party/blink/renderer/core/frame/visual_viewport.h"
+#include "third_party/blink/renderer/core/frame/web_local_frame_impl.h"
 #include "third_party/blink/renderer/core/html/forms/html_form_element.h"
 #include "third_party/blink/renderer/core/html/html_frame_owner_element.h"
 #include "third_party/blink/renderer/core/html_names.h"
@@ -938,8 +939,13 @@ static bool ShouldNavigate(WebNavigationParams* params, LocalFrame* frame) {
   if (MIMETypeRegistry::IsSupportedMIMEType(mime_type))
     return true;
   PluginData* plugin_data = frame->GetPluginData();
-  return !mime_type.IsEmpty() && plugin_data &&
-         plugin_data->SupportsMimeType(mime_type);
+  bool can_load_with_plugin = !mime_type.IsEmpty() && plugin_data &&
+                              plugin_data->SupportsMimeType(mime_type);
+  if (!can_load_with_plugin) {
+    WebLocalFrameImpl::FromFrame(frame)->Client()->WillFailCommitNavigation(
+        WebLocalFrameClient::CommitFailureReason::kNoPluginForMimeType);
+  }
+  return can_load_with_plugin;
 }
 
 void FrameLoader::CommitNavigation(