NetInfo: Slight update to the default network quality value

content/browser/net_info_browsertest.cc

Index: content/browser/net_info_browsertest.cc
diff --git a/content/browser/net_info_browsertest.cc b/content/browser/net_info_browsertest.cc
index e4eec850d7fa659c225611fd3eaa1ad18a8b29a9..6e5042e798d2b4ddfe644485bc91011d6e1ef24f 100644
--- a/content/browser/net_info_browsertest.cc
+++ b/content/browser/net_info_browsertest.cc
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include <cmath>  // For std::modf.
 #include <map>
 #include <string>
 
@@ -95,6 +96,12 @@ class NetInfoBrowserTest : public content::ContentBrowserTest {
     EXPECT_TRUE(base::StringToDouble(RunScriptExtractString(script), &data));
     return data;
   }
+
+  int RunScriptExtractInt(const std::string& script) {
+    int data = 0;
+    EXPECT_TRUE(base::StringToInt(RunScriptExtractString(script), &data));

[nasko, 2017/06/01 22:16:13]

ExecuteScriptAndExtractInt?

[tbansal1, 2017/06/01 23:26:46]

Done.

+    return data;
+  }
 };
 
 // Make sure the type is correct when the page is first opened.
@@ -164,7 +171,8 @@ IN_PROC_BROWSER_TEST_F(NetInfoBrowserTest, TwoRenderViewsInOneProcess) {
 }
 
 // Verify that when the network quality notifications are not sent, the
-// Javascript API returns invalid estimate.
+// Javascript API returns a valid estimate that is multiple of 25 msec and 25
+// kbps.
 IN_PROC_BROWSER_TEST_F(NetInfoBrowserTest,
                        NetworkQualityEstimatorNotInitialized) {
   base::HistogramTester histogram_tester;
@@ -177,9 +185,19 @@ IN_PROC_BROWSER_TEST_F(NetInfoBrowserTest,
   EXPECT_TRUE(
       NavigateToURL(shell(), embedded_test_server()->GetURL("/net_info.html")));
 
-  EXPECT_EQ(0, RunScriptExtractDouble("getRtt()"));
-  EXPECT_EQ(std::numeric_limits<double>::infinity(),
-            RunScriptExtractDouble("getDownlink()"));
+  EXPECT_EQ(0, RunScriptExtractInt("getRtt()"));

[nasko, 2017/06/01 22:16:12]

Why can't ExecuteScriptAndExtractInt be used?

[tbansal1, 2017/06/01 23:26:46]

Can be. RunScriptExtractInt() is slightly easier to use since it directly
returns the int value.

+  EXPECT_EQ(0, RunScriptExtractInt("getRtt()") % 25);
+
+  double downlink_mbps = RunScriptExtractDouble("getDownlink()");

[nasko, 2017/06/01 22:16:13]

Similarly ExecuteScriptAndExtractDouble?

[tbansal1, 2017/06/01 23:26:46]

Same as above. Helper method RunScriptExtractDouble() makes the code slightly
more readable here.

+  EXPECT_LE(0, downlink_mbps);
+
+  double fraction_part, int_part;
+  fraction_part = std::modf(downlink_mbps, &int_part);
+  // If |fraction_part| is 0, it implies |downlink_mbps| is a multiple of 1
+  // Mbps, and hence it is a multiple of 25 kbps.
+  EXPECT_TRUE(static_cast<int>(downlink_mbps * 1000) % 25 == 0 ||

[nasko, 2017/06/01 22:16:12]

Shouldn't we be dividing the mbps to get kbps instead of multiplying it to get
gbps?

[tbansal1, 2017/06/01 23:26:46]

nope, multiplying it by 1000 would give kbps.
We want to verify if getDownlink() is a multiple of 0.025 mbps (i.e., 25 kbps).
So, e.g., if getDownlink() returns 1.275, then we multiple by 1000 and then take
mod 25.

[nasko, 2017/06/03 00:09:47]

Well, when you have mbps and multiply by 1000, you get gbps, don't you? Maybe we
are using different terminology.
That statement will always be true though. X * 1000 % 25 is guaranteed to be 0.
It is so, be cause it can be represented as (X * 40 * 25) % 25. Any multiple of
25 will be 0 mod 25.

[tbansal1, 2017/06/05 13:52:20]

We probably are.
|downlink_mbps| is a double. Let's say calling the netinfo API returns that
bandwidth is 1.23456 mbps. 
So, |downlink_mbps| would be set to 1.23456. If the caller wants to know the
speed in kbps, it needs to multiple |downlink_mbps| by 1000, which will give us
1234.56 kbps (same as 1.23456 mbps).
Right but only if X was a int which is not the case here. Here, X is a double.
e.g., if X is 1.23456, then 
static_cast<int>(X * 1000)  will be 1234 which is not a multiple of 25.
Let me know if you have suggestions for improving the readability. Sorry for the
confusion.

[nasko, 2017/06/05 23:43:01]

Thanks for the explanation. If you were to only multiply the fractional part, it
probably would've been a bit more clear, as 1mb is always multiple of 25kb.
Also, including in a comment an example is always helpful to see.

+              fraction_part == 0);
+
   EXPECT_EQ("4g", RunScriptExtractString("getEffectiveType()"));
 }
 
@@ -249,7 +267,7 @@ IN_PROC_BROWSER_TEST_F(NetInfoBrowserTest, NetworkQualityChangeNotified) {
       histogram_tester.GetAllSamples("NQE.RenderThreadNotified").empty());
 
   EXPECT_EQ(network_quality_1.transport_rtt().InMilliseconds(),
-            RunScriptExtractDouble("getRtt()"));
+            RunScriptExtractInt("getRtt()"));
   EXPECT_EQ(
       static_cast<double>(network_quality_1.downstream_throughput_kbps()) /
           1000,
@@ -262,7 +280,7 @@ IN_PROC_BROWSER_TEST_F(NetInfoBrowserTest, NetworkQualityChangeNotified) {
       network_quality_2);
   base::RunLoop().RunUntilIdle();
   EXPECT_EQ(network_quality_2.transport_rtt().InMilliseconds(),
-            RunScriptExtractDouble("getRtt()"));
+            RunScriptExtractInt("getRtt()"));
   EXPECT_EQ(
       static_cast<double>(network_quality_2.downstream_throughput_kbps()) /
           1000,
@@ -289,7 +307,7 @@ IN_PROC_BROWSER_TEST_F(NetInfoBrowserTest, NetworkQualityChangeRounded) {
   EXPECT_TRUE(embedded_test_server()->Start());
   EXPECT_TRUE(
       NavigateToURL(shell(), embedded_test_server()->GetURL("/net_info.html")));
-  EXPECT_EQ(200, RunScriptExtractDouble("getRtt()"));
+  EXPECT_EQ(200, RunScriptExtractInt("getRtt()"));
   EXPECT_EQ(0.300, RunScriptExtractDouble("getDownlink()"));
 
   net::nqe::internal::NetworkQuality network_quality_2(
@@ -298,7 +316,7 @@ IN_PROC_BROWSER_TEST_F(NetInfoBrowserTest, NetworkQualityChangeRounded) {
   estimator.NotifyObserversOfRTTOrThroughputEstimatesComputed(
       network_quality_2);
   base::RunLoop().RunUntilIdle();
-  EXPECT_EQ(1225, RunScriptExtractDouble("getRtt()"));
+  EXPECT_EQ(1225, RunScriptExtractInt("getRtt()"));
   EXPECT_EQ(1.325, RunScriptExtractDouble("getDownlink()"));
 
   net::nqe::internal::NetworkQuality network_quality_3(
@@ -307,7 +325,7 @@ IN_PROC_BROWSER_TEST_F(NetInfoBrowserTest, NetworkQualityChangeRounded) {
   estimator.NotifyObserversOfRTTOrThroughputEstimatesComputed(
       network_quality_3);
   base::RunLoop().RunUntilIdle();
-  EXPECT_EQ(0, RunScriptExtractDouble("getRtt()"));
+  EXPECT_EQ(0, RunScriptExtractInt("getRtt()"));
   EXPECT_EQ(0, RunScriptExtractDouble("getDownlink()"));
 }
 
@@ -329,7 +347,7 @@ IN_PROC_BROWSER_TEST_F(NetInfoBrowserTest, NetworkQualityChangeNotNotified) {
   EXPECT_TRUE(embedded_test_server()->Start());
   EXPECT_TRUE(
       NavigateToURL(shell(), embedded_test_server()->GetURL("/net_info.html")));
-  EXPECT_EQ(1200, RunScriptExtractDouble("getRtt()"));
+  EXPECT_EQ(1200, RunScriptExtractInt("getRtt()"));
   EXPECT_EQ(1.300, RunScriptExtractDouble("getDownlink()"));
 
   // All the 3 metrics change by less than 10%. So, the observers are not
@@ -340,7 +358,7 @@ IN_PROC_BROWSER_TEST_F(NetInfoBrowserTest, NetworkQualityChangeNotNotified) {
   estimator.NotifyObserversOfRTTOrThroughputEstimatesComputed(
       network_quality_2);
   base::RunLoop().RunUntilIdle();
-  EXPECT_EQ(1200, RunScriptExtractDouble("getRtt()"));
+  EXPECT_EQ(1200, RunScriptExtractInt("getRtt()"));
   EXPECT_EQ(1.300, RunScriptExtractDouble("getDownlink()"));
 
   // Transport RTT has changed by more than 10% from the last notified value of
@@ -351,7 +369,7 @@ IN_PROC_BROWSER_TEST_F(NetInfoBrowserTest, NetworkQualityChangeNotNotified) {
   estimator.NotifyObserversOfRTTOrThroughputEstimatesComputed(
       network_quality_3);
   base::RunLoop().RunUntilIdle();
-  EXPECT_EQ(2300, RunScriptExtractDouble("getRtt()"));
+  EXPECT_EQ(2300, RunScriptExtractInt("getRtt()"));
   EXPECT_EQ(1.400, RunScriptExtractDouble("getDownlink()"));
 }