Use messages for (some) public API errors

pkg/front_end/messages.yaml

Index: pkg/front_end/messages.yaml
diff --git a/pkg/front_end/messages.yaml b/pkg/front_end/messages.yaml
index 70a573e0dd052b2af81da76e2758f25aaf34c287..4998afb3e3819297af89bfa189d4f019826c8c9f 100644
--- a/pkg/front_end/messages.yaml
+++ b/pkg/front_end/messages.yaml
@@ -549,3 +549,23 @@ FastaUsageLong:
 
 FastaCLIArgumentRequired:
   template: "Expected value after '#name'."
+
+MissingMain:
+  template: "No 'main' method found."
+  tip: "Try adding a method named 'main' to your program."
+  dart2jsCode: MISSING_MAIN
+
+MissingInputFile:
+  template: "Input file not found: #string."
+
+MissingSdkRoot:
+  template: "SDK root directory not found: #string."
+
+MissingSdkSummary:
+  template: "SDK summary not found: #string."
+
+CombinedCompileSdkAndSummary:
+  template: "The compileSdk and sdkSummary options are mutually exclusive"
+
+VerificationError:
+  template: "An internal error was found while verifying the output of the compiler. #string"