Fix a crash when processing an invalid PAC script.

net/proxy/proxy_resolver_v8.cc

Index: net/proxy/proxy_resolver_v8.cc
diff --git a/net/proxy/proxy_resolver_v8.cc b/net/proxy/proxy_resolver_v8.cc
index 2bb858c46ead631ed73d9cdedd77756b9501f0f5..57d68b5d8f9af105ff66644307665e74b9dffe31 100644
--- a/net/proxy/proxy_resolver_v8.cc
+++ b/net/proxy/proxy_resolver_v8.cc
@@ -431,11 +431,9 @@ class ProxyResolverV8::Context {
     v8::Context::Scope function_scope(context);
 
     v8::Local<v8::Value> function;
-    if (!GetFindProxyForURL(&function)) {
-      js_bindings()->OnError(
-          -1, base::ASCIIToUTF16("FindProxyForURL() is undefined."));
-      return ERR_PAC_SCRIPT_FAILED;
-    }
+    int rv = GetFindProxyForURL(&function);
+    if (rv != OK)
+      return rv;
 
     v8::Local<v8::Value> argv[] = {
       ASCIIStringToV8String(isolate_, query_url.spec()),
@@ -561,23 +559,41 @@ class ProxyResolverV8::Context {
     // At a minimum, the FindProxyForURL() function must be defined for this
     // to be a legitimiate PAC script.
     v8::Local<v8::Value> function;
-    if (!GetFindProxyForURL(&function)) {
-      js_bindings()->OnError(
-          -1, base::ASCIIToUTF16("FindProxyForURL() is undefined."));
-      return ERR_PAC_SCRIPT_FAILED;
-    }
-
-    return OK;
+    return GetFindProxyForURL(&function);
   }
 
  private:
-  bool GetFindProxyForURL(v8::Local<v8::Value>* function) {
+  int GetFindProxyForURL(v8::Local<v8::Value>* function) {
     v8::Local<v8::Context> context =
         v8::Local<v8::Context>::New(isolate_, v8_context_);
+
+    v8::TryCatch try_catch;
+
     *function =
         context->Global()->Get(
             ASCIILiteralToV8String(isolate_, "FindProxyForURL"));
-    return (*function)->IsFunction();
+
+    if (try_catch.HasCaught())
+      HandleError(try_catch.Message());
+
+    // The value should only be empty if an exception was thrown. Code
+    // defensively just in case.
+    DCHECK_EQ(function->IsEmpty(), try_catch.HasCaught());
+    if (function->IsEmpty() || try_catch.HasCaught()) {
+      js_bindings()->OnError(
+          -1,
+          base::ASCIIToUTF16("Accessing FindProxyForURL threw an exception."));
+      return ERR_PAC_SCRIPT_FAILED;
+    }
+
+    if (!(*function)->IsFunction()) {
+      js_bindings()->OnError(
+          -1, base::ASCIIToUTF16(
+                  "FindProxyForURL is undefined or not a function."));
+      return ERR_PAC_SCRIPT_FAILED;
+    }
+
+    return OK;
   }
 
   // Handle an exception thrown by V8.