Fix chrome os flakyness for test ExtensionApiTest.CaptureVisibleTab....

chrome/test/data/extensions/api_test/tabs/capture_visible_tab/test.js

 // tabs api test
 // browser_tests.exe --gtest_filter=ExtensionApiTest.CaptureVisibleTab
 
 var pass = chrome.test.callbackPass;
 var assertEq = chrome.test.assertEq;
 var assertTrue = chrome.test.assertTrue;
 
-function pageUrl(letter) {
-  return chrome.extension.getURL(letter + ".html");
+var kWidth = 400;
+var kHeight = 400;
+
+function pageUrl(base) {
+  return chrome.extension.getURL(base + ".html");
 }
 
+function testAllPixelsAreExpectedColor(imgUrl, color) {
+  assertEq("string", typeof(imgUrl));
+  var img = new Image();
+  img.width = kWidth;
+  img.height = kHeight;
+  img.src = imgUrl;
+  img.onload = pass(function() {
+    var canvas = document.createElement("canvas");
+
+    // Comparing pixels is slow enough to hit timeouts.  Compare
+    // a 10x10 region.
+    canvas.setAttribute('width', 10);
+    canvas.setAttribute('height', 10);
+    var context = canvas.getContext('2d');
+    context.drawImage(img, 0, 0, 10, 10);
+
+    var imageData = context.getImageData(1, 1, 9, 9).data;
+
+    var badPixels = [];
+
+    for (var i = 0, n = imageData.length; i < n; i += 4) {
+      if (color[0] != imageData[i+0] ||
+          color[1] != imageData[i+1] ||
+          color[2] != imageData[i+2] ||
+          color[3] != imageData[i+3] ) {
+        badPixels.push({"i": i,
+                        "color": [imageData[i+0], imageData[i+1],
+                                  imageData[i+2], imageData[i+3]]
+                       });
+      }
+    }
+    assertEq("[]", JSON.stringify(badPixels, null, 2))
+  });
+}
+
+// Globals used to allow a test to read data from a previous test.
+var blackImageUrl;
+var whiteImageUrl;
+
 chrome.test.runTests([
   // Open a window with one tab, take a snapshot.
-  function captureVisibleTabSimple() {
+  function captureVisibleTabWhiteImage() {
     // Keep the resulting image small by making the window small.
-    createWindow([pageUrl("a")], {"width": 300, "height": 150},
+    createWindow([pageUrl("white")], {"width": kWidth, "height": kHeight},
                  pass(function(winId, tabIds) {
       waitForAllTabs(pass(function() {
         chrome.tabs.getSelected(winId, pass(function(tab) {
           assertEq('complete', tab.status);  // waitForAllTabs ensures this.
           chrome.tabs.captureVisibleTab(winId, pass(function(imgDataUrl) {
             // The URL should be a data URL with has a JPEG mime type.
             assertEq("string", typeof(imgDataUrl));
             assertEq('data:image/jpg;base64,', imgDataUrl.substr(0,22));
+            whiteImageUrl = imgDataUrl;
+
+            testAllPixelsAreExpectedColor(whiteImageUrl,
+                                          [255, 255, 255, 255]);  // White.
           }));
         }));
       }));
     }));
   },
 
-  // Open a window with three tabs, take a snapshot of each.
-  function captureVisibleTabMultiTab() {
-    var snapshotAndRemoveSelectedTab = function(winId, callback) {
-      chrome.tabs.getSelected(winId, function(tab) {
-        chrome.tabs.captureVisibleTab(winId, function(imgDataUrl) {
-          // Test that the URL we got is a data URL which encodes a JPEG image.
-          assertEq("string", typeof(imgDataUrl));
-          assertEq('data:image/jpg;base64,', imgDataUrl.substr(0,22));
+  function captureVisibleTabBlackImage() {
+    // Keep the resulting image small by making the window small.
+    createWindow([pageUrl("black")], {"width": kWidth, "height": kHeight},
+                 pass(function(winId, tabIds) {
+      waitForAllTabs(pass(function() {
+        chrome.tabs.getSelected(winId, pass(function(tab) {
+          assertEq('complete', tab.status);  // waitForAllTabs ensures this.
+          chrome.tabs.captureVisibleTab(winId, pass(function(imgDataUrl) {
+            // The URL should be a data URL with has a JPEG mime type.
+            assertEq("string", typeof(imgDataUrl));
+            assertEq('data:image/jpg;base64,', imgDataUrl.substr(0,22));
+            blackImageUrl = imgDataUrl;
 
-          // TODO(skerner): Once an option allows captureVisibleTab to
-          // take a lossless snapshot with a set color depth, use
-          // a canvas to compare |imgDataUrl| to an image of the tab
-          // we expect.  This can't be done with JPEG, as the results
-          // vary based on the display settings.
-          chrome.tabs.remove(tab.id, callback);
-        });
-      });
-    };
+            // Check that previous capture was done.
+            assertEq('string', typeof(whiteImageUrl));
 
-    createWindow(["a", "b", "c"].map(pageUrl), {"width": 300, "height": 150},
-      function(winId, tabIds){
-        waitForAllTabs(pass(function() {
-          snapshotAndRemoveSelectedTab(winId, pass(function() {
-            snapshotAndRemoveSelectedTab(winId, pass(function() {
-              snapshotAndRemoveSelectedTab(winId, pass(function() {}));
-            }));
+            assertTrue(whiteImageUrl != blackImageUrl);
+
+            testAllPixelsAreExpectedColor(blackImageUrl,
+                                          [0, 0, 0, 255]);  // Black.
           }));
         }));
-      });
+      }));
+    }));
+  },
+
+  function captureVisibleTabRedPng() {
+    // Keep the resulting image small by making the window small.
+    createWindow([pageUrl("red")], {"width": kWidth, "height": kHeight},
+                 pass(function(winId, tabIds) {
+      waitForAllTabs(pass(function() {
+        chrome.tabs.getSelected(winId, pass(function(tab) {
+          assertEq('complete', tab.status);  // waitForAllTabs ensures this.
+          chrome.tabs.captureVisibleTab(winId,
+                                        {"format": "png"},
+                                        pass(function(imgDataUrl) {
+            // The URL should be a data URL with has a PNG mime type.
+            assertEq("string", typeof(imgDataUrl));
+            assertEq('data:image/png;base64,', imgDataUrl.substr(0,22));
+
+            // TODO(skerner): The pixel comparison test fails on XP.
+            // Find out why.
+            //testAllPixelsAreExpectedColor(imgDataUrl,
+            //                              [255, 0, 0, 255]);  // Red.
+          }));
+        }));
+      }));
+    }));
   }
 ]);