Fix flaky BraveWalletSignMessageBrowserTest.SIWE test (#34285)

* Fix flaky BraveWalletSignMessageBrowserTest.SIWE test

The SIWE test sends two sign messages per iteration: one with matching
origin and one with a different origin ("www.a.com"). The second message
is rejected immediately by the provider, overwriting the global
signMessageResult variable with an error. After
NotifySignMessageRequestProcessed approves the first message, the test
immediately checked signMessageResult, but the mojo approval response
may not have been delivered to the renderer yet, so signMessageResult
still contained the rejection error.

Fix by replacing the immediate getSignMessageResult() check with a
Promise-based wait that polls until signMessageResult is a string
starting with "0x" (the signature). This is safe because both the
rejection and approval go through the same mojo interface, so the
rejection always arrives before the approval.

Resolves brave/brave-browser#53167

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Address review: fix same race condition in other sign message tests

Apply the same async polling pattern to UserApprovedRequest and
UserRejectedRequest tests, which had the same race condition of
calling getSignMessageResult() immediately after
NotifySignMessageRequestProcessed() without waiting for the mojo
response to arrive at the renderer.

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: 2 people

browser/brave_wallet/brave_wallet_sign_message_browsertest.cc

@@ -37,6 +37,27 @@ namespace brave_wallet {
 
 namespace {
 
+// Waits for signMessageResult to be set to a string value. After
+// NotifySignMessageRequestProcessed() the result is delivered asynchronously
+// to the renderer via mojo, so we must poll rather than reading it immediately.
+constexpr char kWaitForSignMessageResult[] = R"(
+    new Promise((resolve, reject) => {
+      const deadline = Date.now() + 10000;
+      const check = () => {
+        if (typeof signMessageResult === 'string') {
+          const result = signMessageResult;
+          signMessageResult = undefined;
+          resolve(result);
+        } else if (Date.now() >= deadline) {
+          reject(new Error('Timeout: signMessageResult=' +
+                           signMessageResult));
+        } else {
+          setTimeout(check, 10);
+        }
+      };
+      check();
+    }))";
+
 bool WaitForWalletBubble(content::WebContents* web_contents) {
   auto* tab_helper =
       brave_wallet::BraveWalletTabHelper::FromWebContents(web_contents);
@@ -168,7 +189,7 @@ IN_PROC_BROWSER_TEST_F(BraveWalletSignMessageBrowserTest, UserApprovedRequest) {
     EXPECT_TRUE(WaitForWalletBubble(web_contents()));
     brave_wallet_service()->NotifySignMessageRequestProcessed(
         true, request_index++, nullptr, std::nullopt);
-    EXPECT_EQ(EvalJs(web_contents(), "getSignMessageResult()").ExtractString(),
+    EXPECT_EQ(EvalJs(web_contents(), kWaitForSignMessageResult).ExtractString(),
               "0x670651c072cac2a3f93cb862a17378f6849c66b4516e5d5a30210868a2840e"
               "2a6a345a"
               "4f84615c591c1a47260e798babe8f2f0cce03a09dac09df79c55d8e4401b");
@@ -196,7 +217,7 @@ IN_PROC_BROWSER_TEST_F(BraveWalletSignMessageBrowserTest, UserRejectedRequest) {
     EXPECT_TRUE(WaitForWalletBubble(web_contents()));
     brave_wallet_service()->NotifySignMessageRequestProcessed(
         false, request_index++, nullptr, std::nullopt);
-    EXPECT_EQ(EvalJs(web_contents(), "getSignMessageResult()").ExtractString(),
+    EXPECT_EQ(EvalJs(web_contents(), kWaitForSignMessageResult).ExtractString(),
               l10n_util::GetStringUTF8(IDS_WALLET_USER_REJECTED_REQUEST));
   }
 }
@@ -334,8 +355,30 @@ IN_PROC_BROWSER_TEST_F(BraveWalletSignMessageBrowserTest, SIWE) {
       EXPECT_TRUE(WaitForWalletBubble(web_contents()));
       brave_wallet_service()->NotifySignMessageRequestProcessed(
           true, request_index++, nullptr, std::nullopt);
+      // The second sign message (wrong origin) is rejected immediately,
+      // overwriting signMessageResult with an error before the approved
+      // first message's signature arrives via mojo. Wait for the signature
+      // (starts with "0x") to be delivered to the renderer.
+      static constexpr char kWaitForSignResult[] = R"(
+        new Promise((resolve, reject) => {
+          const deadline = Date.now() + 10000;
+          const check = () => {
+            if (typeof signMessageResult === 'string' &&
+                signMessageResult.startsWith('0x')) {
+              const result = signMessageResult;
+              signMessageResult = undefined;
+              resolve(result);
+            } else if (Date.now() >= deadline) {
+              reject(new Error('Timeout: signMessageResult=' +
+                               signMessageResult));
+            } else {
+              setTimeout(check, 10);
+            }
+          };
+          check();
+        }))";
       // port is dynamic
-      EXPECT_TRUE(EvalJs(web_contents(), "getSignMessageResult()")
+      EXPECT_TRUE(EvalJs(web_contents(), kWaitForSignResult)
                       .ExtractString()
                       .starts_with("0x"));
     }