Merge a number of assertion failure fixes to the 3.0 branch.

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
===================================================================
--- src/x64/full-codegen-x64.cc	(revision 6703)
+++ src/x64/full-codegen-x64.cc	(working copy)
@@ -245,19 +245,22 @@
     // patch with the code required by the debugger.
     __ movq(rsp, rbp);
     __ pop(rbp);
-    __ ret((scope()->num_parameters() + 1) * kPointerSize);
+
+    int arguments_bytes = (scope()->num_parameters() + 1) * kPointerSize;
+    __ Ret(arguments_bytes, rcx);
+
 #ifdef ENABLE_DEBUGGER_SUPPORT
     // Add padding that will be overwritten by a debugger breakpoint.  We
-    // have just generated "movq rsp, rbp; pop rbp; ret k" with length 7
+    // have just generated at least 7 bytes: "movq rsp, rbp; pop rbp; ret k"
     // (3 + 1 + 3).
     const int kPadding = Assembler::kJSReturnSequenceLength - 7;
     for (int i = 0; i < kPadding; ++i) {
       masm_->int3();
     }
-    // Check that the size of the code used for returning matches what is
-    // expected by the debugger.
-    ASSERT_EQ(Assembler::kJSReturnSequenceLength,
-            masm_->SizeOfCodeGeneratedSince(&check_exit_codesize));
+    // Check that the size of the code used for returning is large enough
+    // for the debugger's requirements.
+    ASSERT(Assembler::kJSReturnSequenceLength <=
+           masm_->SizeOfCodeGeneratedSince(&check_exit_codesize));
 #endif
   }
 }