Throw IOException at source of failing to open a dex file.

Before is:
java.lang.ClassNotFoundException: Didn't find class "GCBench" on path: DexPathList[[zip file "/disk2/dalvik-dev/out/host/linux-x86/framework/GCBench.jar"],nativeLibraryDirectories=[/disk2/dalvik-dev/out/host/linux-x86/lib]]
        at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:511)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:469)
        Suppressed: java.lang.ClassNotFoundException: GCBench
                at java.lang.Class.classForName(Native Method)
                at java.lang.BootClassLoader.findClass(ClassLoader.java:781)
                at java.lang.BootClassLoader.loadClass(ClassLoader.java:841)
                at java.lang.ClassLoader.loadClass(ClassLoader.java:504)
                ... 1 more
        Caused by: java.lang.NoClassDefFoundError: Class "LGCBench;" not found
                ... 5 more
And after is:
java.lang.ClassNotFoundException: Didn't find class "GCBench" on path: DexPathList[[zip file "/disk2/dalvik-dev/out/host/linux-x86/framework/GCBench.jar"],nativeLibraryDirectories=[/disk2/dalvik-dev/out/host/linux-x86/lib]]
        at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:511)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:469)
        Suppressed: java.io.IOException: Zip archive '/disk2/dalvik-dev/out/host/linux-x86/framework/GCBench.jar' doesn't contain classes.dex
                at dalvik.system.DexFile.openDexFile(Native Method)
                at dalvik.system.DexFile.<init>(DexFile.java:80)
                at dalvik.system.DexFile.<init>(DexFile.java:59)
                at dalvik.system.DexPathList.loadDexFile(DexPathList.java:268)
                at dalvik.system.DexPathList.makeDexElements(DexPathList.java:235)
                at dalvik.system.DexPathList.<init>(DexPathList.java:113)
                at dalvik.system.BaseDexClassLoader.<init>(BaseDexClassLoader.java:48)
                at dalvik.system.PathClassLoader.<init>(PathClassLoader.java:38)
                at java.lang.ClassLoader.createSystemClassLoader(ClassLoader.java:128)
                at java.lang.ClassLoader.access$000(ClassLoader.java:65)
                at java.lang.ClassLoader$SystemClassLoader.<clinit>(ClassLoader.java:81)
                at java.lang.ClassLoader.getSystemClassLoader(ClassLoader.java:137)
        Suppressed: java.lang.ClassNotFoundException: GCBench
                at java.lang.Class.classForName(Native Method)
                at java.lang.BootClassLoader.findClass(ClassLoader.java:781)
                at java.lang.BootClassLoader.loadClass(ClassLoader.java:841)
                at java.lang.ClassLoader.loadClass(ClassLoader.java:504)
                ... 1 more
        Caused by: java.lang.NoClassDefFoundError: Class "LGCBench;" not found
                ... 5 more

Also, move dex file verifier messages out of logs.
In the process the ClassLinker::dex_lock_ needed tidying to cover a smaller
scope. Bug 11301553.

Change-Id: I80058652e11e7ea63457cc01a0cb48afe1c15543
diff --git a/compiler/image_writer.cc b/compiler/image_writer.cc
index bcdc1c1..871cfd5 100644
--- a/compiler/image_writer.cc
+++ b/compiler/image_writer.cc
@@ -82,12 +82,14 @@
     LOG(ERROR) << "Failed to open oat file " << oat_filename << " for " << oat_location;
     return false;
   }
-  oat_file_ = OatFile::OpenWritable(oat_file.get(), oat_location);
-  if (oat_file_ == NULL) {
-    LOG(ERROR) << "Failed to open writable oat file " << oat_filename << " for " << oat_location;
+  std::string error_msg;
+  oat_file_ = OatFile::OpenWritable(oat_file.get(), oat_location, &error_msg);
+  if (oat_file_ == nullptr) {
+    LOG(ERROR) << "Failed to open writable oat file " << oat_filename << " for " << oat_location
+        << ": " << error_msg;
     return false;
   }
-  class_linker->RegisterOatFile(*oat_file_);
+  CHECK_EQ(class_linker->RegisterOatFile(oat_file_), oat_file_);
 
   interpreter_to_interpreter_bridge_offset_ =
       oat_file_->GetOatHeader().GetInterpreterToInterpreterBridgeOffset();
@@ -192,9 +194,10 @@
 
   int prot = PROT_READ | PROT_WRITE;
   size_t length = RoundUp(size, kPageSize);
-  image_.reset(MemMap::MapAnonymous("image writer image", NULL, length, prot));
-  if (image_.get() == NULL) {
-    LOG(ERROR) << "Failed to allocate memory for image file generation";
+  std::string error_msg;
+  image_.reset(MemMap::MapAnonymous("image writer image", NULL, length, prot, &error_msg));
+  if (UNLIKELY(image_.get() == nullptr)) {
+    LOG(ERROR) << "Failed to allocate memory for image file generation: " << error_msg;
     return false;
   }
   return true;