Add UMA for testing whether device supports memory mapping APK files with executable permissions.

base/android/java/src/org/chromium/base/library_loader/Linker.java

Index: base/android/java/src/org/chromium/base/library_loader/Linker.java
diff --git a/base/android/java/src/org/chromium/base/library_loader/Linker.java b/base/android/java/src/org/chromium/base/library_loader/Linker.java
index 2a3006ad174741b127dd62194b72abfbd2e21bf1..f42e04f8c7e23dc1f5d9c455cff20b96bee59fc2 100644
--- a/base/android/java/src/org/chromium/base/library_loader/Linker.java
+++ b/base/android/java/src/org/chromium/base/library_loader/Linker.java
@@ -136,7 +136,7 @@ import javax.annotation.Nullable;
  *
  *    This behaviour is altered by the BROWSER_SHARED_RELRO_CONFIG configuration
  *    variable below, which may force the browser to load the libraries at
- *    fixed addresses to.
+ *    fixed addresses too.
  *
  *  - Once all libraries are loaded in the browser process, one can call
  *    getSharedRelros() which returns a Bundle instance containing a map that
@@ -221,6 +221,10 @@ public class Linker {
     // Becomes true once prepareLibraryLoad() has been called.
     private static boolean sPrepareLibraryLoadCalled = false;
 
+    // One-way switch recording whether the device supports memory mapping
+    // APK files with executable permissions.
+    private static boolean sLoadFromApkSucceeded = false;
+

[picksi1, 2014/10/10 10:52:17]

Is this really a bool? Should this be an enum that defines the possible states?
e.g. LOAD_NOT_ATTEMPTED, LOAD_FAILED_DUE_TO_MISSING_FILE,
LOAD_FAILED_DUE_TO_PERMISSIONS, LOAD_SUCCESSFUL?

[petrcermak, 2014/10/10 14:20:14]

As discussed, we will keep the boolean because we consider only two possible
states (supported, not supported) and it simplifies code (if we used an enum, we
would essentially need to define it twice because of the native call).

     // Used internally to initialize the linker's static data. Assume lock is held.
     private static void ensureInitializedLocked() {
         assert Thread.holdsLock(Linker.class);
@@ -837,6 +841,35 @@ public class Linker {
     }
 
     /**
+     * Test whether the device supports memory mapping APK files with executable
+     * permissions.
+     *
+     * @param apkFile Filename of the APK.
+     * @return true if supported.
+     */
+    public static void testLoadFromApk(String apkFile) {
+        synchronized (Linker.class) {
+            ensureInitializedLocked();
+            if (sInBrowserProcess) {
+                if (DEBUG) Log.i(TAG, "testLoadFromApk: " + apkFile);
+                sLoadFromApkSucceeded = nativeTestLoadFromApk(apkFile);
+                if (DEBUG) Log.i(TAG, "Memory mapping APK files with executable permissions " +
+                        (sLoadFromApkSucceeded ? "supported" : "NOT supported"));
+            }
+        }
+    }
+
+    /**
+     * Returns whether the device supports memory mapping APK files with
+     * executable permissions.
+     *
+     * @return true if supported.
+     */
+    public static boolean loadFromApkSucceeded() {
+        return sLoadFromApkSucceeded;

[rmcilroy, 2014/10/10 10:27:05]

Simon's CL moves from storing the result as a static in Linker.java to storing
the result in LibraryLoader.java - I would prefer you follow the same way for
this change.

[petrcermak, 2014/10/10 14:20:14]

Done.

+    }

[picksi1, 2014/10/10 10:52:17]

return sAPKStatus == LOADING_SUCCESSFUL ? Or (my favourite pattern!) replace
this with a check function that you call with an enum, so you can say:

if (IsLoadFromAPKStatus(LOADING_SUCCESSFUL))?

[petrcermak, 2014/10/10 14:20:14]

As explained above, we stick with the boolean type.

+
+    /**
      * Move activity from the native thread to the main UI thread.
      * Called from native code on its own thread.  Posts a callback from
      * the UI thread back to native code.
@@ -934,6 +967,16 @@ public class Linker {
     private static native long nativeGetRandomBaseLoadAddress(long sizeBytes);
 
     /**
+     * Native method which tests whether the device supports memory mapping APK
+     * files with executable permissions
+     *
+     * @param apkFile Filename of the APK.
+     * @return true if supported.
+     *
+     */
+    private static native boolean nativeTestLoadFromApk(String apkFile);
+
+    /**
      * Record information for a given library.
      * IMPORTANT: Native code knows about this class's fields, so
      * don't change them without modifying the corresponding C++ sources.