Fix content verification code for undreadable and deleted files.

extensions/browser/extension_protocols.cc

Index: extensions/browser/extension_protocols.cc
diff --git a/extensions/browser/extension_protocols.cc b/extensions/browser/extension_protocols.cc
index 551064cbd784250c1073044c80fd3b3f5fb5c512..805a9f99b1f80af2bb207c339075d9e88c89cf5e 100644
--- a/extensions/browser/extension_protocols.cc
+++ b/extensions/browser/extension_protocols.cc
@@ -237,6 +237,17 @@ class URLRequestExtensionJob : public net::URLRequestFileJob {
     URLRequestFileJob::SetExtraRequestHeaders(headers);
   }
 
+  void OnOpenComplete(int result) override {
+    if (result < 0) {
+      // File open failure. |result| is net:: error code.

[Devlin, 2017/03/24 18:50:09]

Let's expand on this a bit - something like:
// This can happen when the file is unreadable (which can happen during
// corruption or third-party interaction), or when the file itself is
// empty. In both of these cases, we need to be sure to inform the
// verification job that we've finished reading so that it can proceed;
// see crbug.com/nnn.

[lazyboy, 2017/03/24 19:22:55]

Done.
The empty case is crbug.com/703892, which is a bug in URLRequestFileJob.

+      if (verify_job_.get()) {
+        std::string tmp;
+        verify_job_->BytesRead(0, base::string_as_array(&tmp));
+        verify_job_->DoneReading();
+      }
+    }
+  }
+
   void OnSeekComplete(int64_t result) override {
     DCHECK_EQ(seek_position_, 0);
     seek_position_ = result;