[ScriptStreaming] Fix incorrect DCHECK.

ready_state_ could be kErrorOccured as well as kReadyStreaming. Update the
logic to check for this and add a new NotStreamingReason to log it.

BUG=chromium:865098,chromium:871276

Change-Id: I7f4e17c843b74632d4cf167664f26fdb92f30a8c
Reviewed-on: https://chromium-review.googlesource.com/1164943
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581882}

third_party/blink/renderer/bindings/core/v8/script_streamer.h

@@ -51,6 +51,7 @@ class CORE_EXPORT ScriptStreamer final
     kStreamerNotReadyOnGetSource,
     kInlineScript,
     kDidntTryToStartStreaming,
+    kErrorOccurred,
 
     // Pseudo values that should never be seen in reported metrics
     kCount,

third_party/blink/renderer/core/inspector/inspector_trace_events.cc

@@ -384,6 +384,8 @@ const char* NotStreamedReasonString(ScriptStreamer::NotStreamingReason reason) {
       return "inline script";
     case ScriptStreamer::kDidntTryToStartStreaming:
       return "start streaming not called";
+    case ScriptStreamer::kErrorOccurred:
+      return "an error occurred";
     case ScriptStreamer::kAlreadyLoaded:
     case ScriptStreamer::kCount:
     case ScriptStreamer::kInvalid:

third_party/blink/renderer/core/script/classic_pending_script.cc

@@ -380,11 +380,13 @@ ClassicScript* ClassicPendingScript::GetSource(const KURL& document_url,
     DCHECK_EQ(not_streamed_reason, ScriptStreamer::kInvalid);
     if (streamer_->StreamingSuppressed()) {
       not_streamed_reason = streamer_->StreamingSuppressedReason();
-    } else if (ready_state_ != kReady) {
-      DCHECK_EQ(ready_state_, kReadyStreaming);
+    } else if (ready_state_ == kErrorOccurred) {
+      not_streamed_reason = ScriptStreamer::kErrorOccurred;
+    } else if (ready_state_ == kReadyStreaming) {
       not_streamed_reason = ScriptStreamer::kStreamerNotReadyOnGetSource;
     } else {
       // Streamer can be used to compile script.
+      DCHECK_EQ(ready_state_, kReady);
       streamer_ready = true;
     }
   }

tools/metrics/histograms/enums.xml

@@ -34595,6 +34595,7 @@ Called by update_net_trust_anchors.py.-->
   <int value="10" label="Streamer not ready when GetSource called"/>
   <int value="11" label="Internal script"/>
   <int value="12" label="Streaming was never started"/>
+  <int value="13" label="An error had occurred before GetSource was called"/>
 </enum>
 
 <enum name="NPAPIPluginStatus">