Separate validation failures from other failures in ExecuteCodeFunction.

extensions/browser/api/execute_code_function.h

Index: extensions/browser/api/execute_code_function.h
diff --git a/extensions/browser/api/execute_code_function.h b/extensions/browser/api/execute_code_function.h
index dbf8639e9ff06378db37fc269e8c8c7b1364b5f7..cde98d5b8d8d4a9f694ff3f0dc4ab09c47ab19ee 100644
--- a/extensions/browser/api/execute_code_function.h
+++ b/extensions/browser/api/execute_code_function.h
@@ -6,6 +6,7 @@
 #define EXTENSIONS_BROWSER_API_EXECUTE_CODE_FUNCTION_H_
 
 #include "base/macros.h"
+#include "base/optional.h"
 #include "extensions/browser/extension_function.h"
 #include "extensions/browser/script_executor.h"
 #include "extensions/common/api/extension_types.h"
@@ -27,8 +28,23 @@ class ExecuteCodeFunction : public AsyncExtensionFunction {
   bool HasPermission() override;
   bool RunAsync() override;
 
-  // Initialize |details_| if it hasn't already been.
-  virtual bool Init() = 0;
+  enum InitResult {
+    // ExtensionFunction validation failure.
+    // Warning: Validation failures kill the renderer and should only be used
+    // for circumstances that should never happen.
+    VALIDATION_FAILURE,
+    // Failure other than validation.
+    // Failures return an error to the extension function and should be used
+    // when an error situation occurs: e.g. trying to execute script during
+    // browser shutdown.
+    FAILURE,
+    SUCCESS
+  };
+
+  // Initializes |details_| and other variables if they haven't already been.
+  // Returns whether or not it succeeded. Failure can be tolerable (FAILURE), or
+  // fatal (VALIDATION_FAILURE).
+  virtual InitResult Init() = 0;
   virtual bool ShouldInsertCSS() const = 0;
   virtual bool CanExecuteScriptOnPage() = 0;
   virtual ScriptExecutor* GetScriptExecutor() = 0;
@@ -48,8 +64,20 @@ class ExecuteCodeFunction : public AsyncExtensionFunction {
   const HostID& host_id() const { return host_id_; }
   void set_host_id(const HostID& host_id) { host_id_ = host_id; }
 
+  InitResult set_init_result(InitResult init_result) {
+    init_result_ = init_result;
+    return init_result_.value();
+  }
+  InitResult set_init_result_failure(const std::string& error) {

[Devlin, 2017/01/24 16:09:05]

set_init_result_failure() is a little ambiguous, since we also have validation
failures.  I wonder if we should s/failure/error (and so have validation_failure
and error), for more parity with e.g. SetError(), lastError, et al?

[lazyboy, 2017/01/24 23:36:07]

OK. Done.

+    init_error_ = error;
+    return set_init_result(FAILURE);
+  }
+
   // The injection details.
   std::unique_ptr<api::extension_types::InjectDetails> details_;
+  base::Optional<InitResult> init_result_;
+  // Set iff |init_result_| == FAILURE, holds the error string.
+  base::Optional<std::string> init_error_;
 
  private:
   // Retrieves the file url for the given |extension_path| and optionally