Rationalize and fix chromium android linker histogram recording.

base/android/library_loader/library_loader_hooks.cc

Index: base/android/library_loader/library_loader_hooks.cc
diff --git a/base/android/library_loader/library_loader_hooks.cc b/base/android/library_loader/library_loader_hooks.cc
index 87f791090b0a4cb6607e8457e33adeab1e311aeb..a8c75e1310dc9c93f27f6f95b0f84fd6778de6d8 100644
--- a/base/android/library_loader/library_loader_hooks.cc
+++ b/base/android/library_loader/library_loader_hooks.cc
@@ -19,8 +19,78 @@ base::AtExitManager* g_at_exit_manager = NULL;
 const char* g_library_version_number = "";
 LibraryLoadedHook* g_registration_callback = NULL;
 
+enum RendererHistogramCode {
+  // Renderer load at fixed address success, fail, or not attempted.
+  // Renderers do not attempt to load at at fixed address if on a
+  // low-memory device on which browser load at fixed address has already
+  // failed.
+  LFA_SUCCESS = 0,
+  LFA_BACKOFF_USED = 1,
+  LFA_NOT_ATTEMPTED = 2,
+
+  // End sentinel, also used as nothing-pending indicator.
+  MAX_RENDERER_HISTOGRAM_CODE = 3,
+  NO_PENDING_HISTOGRAM_CODE = MAX_RENDERER_HISTOGRAM_CODE
+};
+
+enum BrowserHistogramCode {
+  // Non-low-memory random address browser loads.
+  NORMAL_LRA_SUCCESS = 0,
+
+  // Low-memory browser loads at fixed address, success or fail.
+  LOW_MEMORY_LFA_SUCCESS = 1,
+  LOW_MEMORY_LFA_BACKOFF_USED = 2,
+
+  MAX_BROWSER_HISTOGRAM_CODE = 3,
+};
+
+RendererHistogramCode g_renderer_histogram_code = NO_PENDING_HISTOGRAM_CODE;
+
 } // namespace
 
+static void RegisterChromiumAndroidLinkerRendererHistogram(
+    JNIEnv* env,
+    jclass clazz,
+    jboolean requested_shared_relro,
+    jboolean load_at_fixed_address_failed) {
+  // Note a pending histogram value for later recording.
+  if (requested_shared_relro) {
+    g_renderer_histogram_code = load_at_fixed_address_failed
+                                ? LFA_BACKOFF_USED : LFA_SUCCESS;
+  } else {
+    g_renderer_histogram_code = LFA_NOT_ATTEMPTED;
+  }
+}
+
+void RecordChromiumAndroidLinkerRendererHistogram() {
+  if (g_renderer_histogram_code == NO_PENDING_HISTOGRAM_CODE)
+    return;
+  // Record and release the pending histogram value.
+  UMA_HISTOGRAM_ENUMERATION("ChromiumAndroidLinker.RendererStates",
+                            g_renderer_histogram_code,
+                            MAX_RENDERER_HISTOGRAM_CODE);
+  g_renderer_histogram_code = NO_PENDING_HISTOGRAM_CODE;
+}

[Ilya Sherman, 2014/10/02 20:53:57]

Why do you need the pending histogram value, rather than just recording this
histogram when the value is set?

[simonb (inactive), 2014/10/03 11:51:42]

The value appears when loading libchrome.so, and this is too early for
histograms to work.  The solution is to save it here as 'pending', and push it
to histograms later and once library code is running.

+
+static void RecordChromiumAndroidLinkerBrowserHistogram(
+    JNIEnv* env,
+    jclass clazz,
+    jboolean is_using_browser_shared_relros,
+    jboolean load_at_fixed_address_failed) {
+  // For low-memory devices, record whether or not we successfully loaded the
+  // browser at a fixed address. Otherwise just record a normal invocation.
+  BrowserHistogramCode histogram_code;
+  if (is_using_browser_shared_relros) {
+    histogram_code = load_at_fixed_address_failed
+                     ? LOW_MEMORY_LFA_BACKOFF_USED : LOW_MEMORY_LFA_SUCCESS;
+  } else {
+    histogram_code = NORMAL_LRA_SUCCESS;
+  }
+  UMA_HISTOGRAM_ENUMERATION("ChromiumAndroidLinker.BrowserStates",
+                            histogram_code,
+                            MAX_BROWSER_HISTOGRAM_CODE);
+}
+
 void SetLibraryLoadedHook(LibraryLoadedHook* func) {
   g_registration_callback = func;
 }
@@ -31,23 +101,12 @@ static void InitCommandLine(JNIEnv* env, jclass clazz,
 }
 
 static jboolean LibraryLoaded(JNIEnv* env, jclass clazz) {
-  if(g_registration_callback == NULL) {
+  if (g_registration_callback == NULL) {
     return true;
   }
   return g_registration_callback(env, clazz);
 }
 
-static void RecordChromiumAndroidLinkerHistogram(
-    JNIEnv* env,
-    jclass clazz,
-    jboolean loaded_at_fixed_address_failed,
-    jboolean is_low_memory_device) {
-  UMA_HISTOGRAM_BOOLEAN("ChromiumAndroidLinker.LoadedAtFixedAddressFailed",
-                        loaded_at_fixed_address_failed);
-  UMA_HISTOGRAM_BOOLEAN("ChromiumAndroidLinker.IsLowMemoryDevice",
-                        is_low_memory_device);

[Ilya Sherman, 2014/10/02 20:53:57]

Please mark the corresponding histograms as <obsolete>

[simonb (inactive), 2014/10/03 11:51:42]

Done.

-}
-
 void LibraryLoaderExitHook() {
   if (g_at_exit_manager) {
     delete g_at_exit_manager;