Random improvements in error reporting.

pkg/front_end/messages.yaml

 # Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # Each entry in this map corresponds to a diagnostic message. Ideally, each
 # entry contains three parts:
 #
 # 1. A message template (template).
 #
 # 2. A suggestion for how to correct the problem (tip).
@@ skipping 612 matching lines @@
 InternalProblemAlreadyInitialized:
   template: "Attempt to set initializer on field without initializer."
 
 InternalProblemBodyOnAbstractMethod:
   template: "Attempting to set body on abstract method."
 
 InternalProblemMissingContext:
   template: "Compiler cannot run without a compiler context."
   tip: "Are calls to the compiler wrapped in CompilerContext.runInContext?"
 
+InternalProblemProvidedBothCompileSdkAndSdkSummary:
+  template: "The compileSdk and sdkSummary options are mutually exclusive"
+
 InternalVerificationError:
   template: "Verification of the generated program failed: #string."
 
 LocalDefinitionHidesExport:
   template: "Local definition of '#name' hides export from '#uri'."
 
 LocalDefinitionHidesImport:
   template: "Local definition of '#name' hides import from '#uri'."
 
 ExportHidesExport:
@@ skipping 162 matching lines @@
 
 MissingMain:
   template: "No 'main' method found."
   tip: "Try adding a method named 'main' to your program."
   dart2jsCode: MISSING_MAIN
 
 MissingInput:
   template: "No input file provided to the compiler."
 
 InputFileNotFound:
-  template: "Input file not found: #string."
+  template: "Input file not found: #uri."
 
 SdkRootNotFound:
-  template: "SDK root directory not found: #string."
+  template: "SDK root directory not found: #uri."
 
 SdkSummaryNotFound:
-  template: "SDK summary not found: #string."
+  template: "SDK summary not found: #uri."
 
 ThisAccessInFieldInitializer:
   template: "Can't access 'this' in a field initializer to read '#name'."
 
 ThisAsIdentifier:
   template: "Expected identifier, but got 'this'."
 
 SuperAsIdentifier:
   template: "Expected identifier, but got 'super'."
 
@@ skipping 54 matching lines @@
 
 CantInferPackagesFromPackageUri:
   template: "Can't infer a .packages file from an input 'package:*' URI."
   tip: "Try specifying the file explicitly with the --packages option."
 
 PackageNotFound:
   template: "Could not resolve the package '#name' in '#uri'."
 
 InvalidPackageUri:
   template: "Invalid package Uri '#uri':\n  #string."