Improve DCHECK error message for web::ExecuteJavaScript.

ios/web/public/test/js_test_util.mm

Index: ios/web/public/test/js_test_util.mm
diff --git a/ios/web/public/test/js_test_util.mm b/ios/web/public/test/js_test_util.mm
index 00ab99d8776797c96f85963a093c90f63d1e11c6..0e474a33633627ded6a7459207d11efbf21d9238 100644
--- a/ios/web/public/test/js_test_util.mm
+++ b/ios/web/public/test/js_test_util.mm
@@ -8,9 +8,10 @@
 
 #include "base/logging.h"
 #import "base/mac/scoped_nsobject.h"
-#import "base/test/ios/wait_util.h"
+#import "ios/testing/wait_util.h"
 #import "ios/web/public/web_state/js/crw_js_injection_manager.h"
 #import "ios/web/public/web_state/js/crw_js_injection_receiver.h"
+#include "testing/gtest/include/gtest/gtest.h"
 
 namespace web {
 
@@ -24,9 +25,15 @@ id ExecuteJavaScript(CRWJSInjectionManager* manager, NSString* script) {
              completed = true;
            }];
 
-  base::test::ios::WaitUntilCondition(^{
-    return completed;
-  });
+  BOOL success = testing::WaitUntilConditionOrTimeout(
+      testing::kWaitForJSCompletionTimeout, ^{
+        return completed;
+      });
+  // Log stack trace to provide some context.
+  EXPECT_TRUE(success)

[michaeldo, 2017/03/03 00:11:00]

I already have another CL in which I'd like to add these lines. WDYT about
adding:

void testing::ExpectCondition(NSTimeInterval interval, ConditionBlock block,
NSString failureMessage)

to ios/testing/wait_util.h

Internally, it can still print the stack so the context will be the same in the
debug output (with the addition of one extra frame., but it would greatly
cleanup the caller code here.

[Eugene But (OOO till 7-30), 2017/03/03 01:48:06]

I believe we should not have different word ("Expect") for the same method and
test assertions should happen in the test, not inside the helper. This CL is an
improvement for sure, but I don't think we should add new functions.

[michaeldo, 2017/03/03 18:17:08]

Acknowledged.

+      << "CRWJSInjectionManager failed to complete javascript execution.\n"
+      << [[[NSThread callStackSymbols] componentsJoinedByString:@"\n"]

[Eugene But (OOO till 7-30), 2017/03/03 01:48:06]

Please use sys_string_conversions.h instead of NSString API (which can return
nil in many cases).

[michaeldo, 2017/03/03 18:17:08]

Of course, thank you.

+             cStringUsingEncoding:NSUTF8StringEncoding];
   return [[result retain] autorelease];
 }
 
@@ -50,9 +57,15 @@ id ExecuteJavaScript(WKWebView* web_view, NSString* script, NSError** error) {
                  *error = [[script_error copy] autorelease];
                completed = true;
              }];
-  base::test::ios::WaitUntilCondition(^{
-    return completed;
-  });
+  BOOL success = testing::WaitUntilConditionOrTimeout(
+      testing::kWaitForJSCompletionTimeout, ^{
+        return completed;
+      });
+  // Log stack trace to provide some context.
+  EXPECT_TRUE(success)
+      << "WKWebView failed to complete javascript execution.\n"
+      << [[[NSThread callStackSymbols] componentsJoinedByString:@"\n"]
+             cStringUsingEncoding:NSUTF8StringEncoding];

[Eugene But (OOO till 7-30), 2017/03/03 01:48:06]

ditto

[michaeldo, 2017/03/03 18:17:08]

Done.

   return [[result retain] autorelease];
 }