Add support for javascript incompatibility warnings.

runtime/vm/exceptions.h

Index: runtime/vm/exceptions.h
===================================================================
--- runtime/vm/exceptions.h	(revision 35994)
+++ runtime/vm/exceptions.h	(working copy)
@@ -14,6 +14,7 @@
 class Class;
 class DartFrameIterator;
 class Error;
+class ICData;
 class Instance;
 class Object;
 class RawInstance;
@@ -21,6 +22,7 @@
 class RawStacktrace;
 class RawObject;
 class Script;
+class StackFrame;
 class String;
 
 class Exceptions : AllStatic {
@@ -30,6 +32,17 @@
   static void Throw(const Instance& exception);
   static void ReThrow(const Instance& exception, const Instance& stacktrace);
   static void PropagateError(const Error& error);
+
+  // Return true if the target function of the given ic_data may check for (and
+  // possibly issue) a Javascript compatibility warning.
+  static bool MayCheckForJSWarning(const ICData& ic_data);
+
+  // Report a Javascript compatibility warning at the call site given by
+  // caller_frame. Note that a JavascriptCompatibilityError is thrown
+  // if --warning_as_error is specified.
+  static void JSWarning(StackFrame* caller_frame, const char* format, ...)
+      PRINTF_ATTRIBUTE(2, 3);
+
   static RawStacktrace* CurrentStacktrace();
 
   // Helpers to create and throw errors.
@@ -55,6 +68,7 @@
     kIsolateSpawn,
     kIsolateUnhandledException,
     kJavascriptIntegerOverflowError,
+    kJavascriptCompatibilityError,
     kAssertion,
     kCast,
     kType,